Timing question

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66corsaguy
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Timing question

Unread post by 66corsaguy » Thu Sep 21, 2017 5:50 pm

1966 Corsa
I want to make sure I understand correctly about timing for my car

My RPM is at 500 and I set timing to 18 after I unplugged and cinched the vacuum tube.

When I attached tube it went down to 16

Is that normal?


There's talk about total timing is that in reference to when you add throttle and RPM goes up advance moves forward and stops somewhere. (It's off the number chart so I don't know what it's at) is that what total advance is?
I want to make sure I set timing correctly but it dropping down to 16 this may be also be because it warmed up?


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terribleted
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Re: Timing question

Unread post by terribleted » Thu Sep 21, 2017 6:07 pm

500 rpm is a bit low..isn't the spec 600 (check the manual). Generally the timing at idle will not go down when connecting the plugged vacuum line it should not really change. (it was plugged when you set the timing wasn't it? (again check the manual it should be removed and plugged). Is it a turbo? If that's the case timing at 16 is way low should be 24 degrees and idle at 850....if it is a turbo the rpm might drop when the vacuum retard is connected if it is active. It should not be active at idle. If it is a 140 then idle RPM should be 600-650 and timing between 16 and 20 before tdc. I find most 140's like near 20. Re-read the chart on page 6-2 of the 65 primary book shop manual for guidance.
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skipvair
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Re: Timing question

Unread post by skipvair » Thu Sep 21, 2017 6:20 pm

Is the vacuum coming from the right port?


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Re: Timing question

Unread post by terribleted » Thu Sep 21, 2017 6:44 pm

skipvair wrote:
Thu Sep 21, 2017 6:20 pm
Is the vacuum coming from the right port?


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good question but unless it is a turbo the timing would go up not down when connected. It really should not change regardless if advance or retard at idle and the correct port is connected..
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Re: Timing question

Unread post by bbodie52 » Fri Sep 22, 2017 7:12 am

66corsaguy wrote:1966 Corsa
I want to make sure I understand correctly about timing for my car

My RPM is at 500 and I set timing to 18 after I unplugged and cinched the vacuum tube.

When I attached tube it went down to 16

Is that normal?

There's talk about total timing is that in reference to when you add throttle and RPM goes up advance moves forward and stops somewhere. (It's off the number chart so I don't know what it's at) is that what total advance is?
I want to make sure I set timing correctly but it dropping down to 16 this may be also be because it warmed up?
The illustrations that I posted below were intended to help illustrate the vacuum advance mechanism, the 140 hp distributor centrifugal and vacuum advance specifications, and the tuneup specifications for your engine. The engine suffix code indicates that it is a 140 hp engine from a 1965-66 Corvair Corsa.

The vacuum advance mechanism moves the breaker plate and ignition points to the right when the vacuum pull is great enough to actuate the vacuum advance. Since the distributor cam rotation his clockwise, moving the points to the right would advance the point where the rubbing block on the ignition points comes into contact with the raised lobe on the distributor cam. The vacuum advance mechanism is normally parked all the way to the left. It would only move to the right when sufficient vacuum was applied to the diaphragm in the vacuum advance mechanism to begin the programmed timing advance. According to the chart the maximum timing advance that would be introduced by the vacuum advance mechanism would be 22° at 14 inches of vacuum. The vacuum advance mechanism cannot normally move the timing associated with location of the breaker plate to the left (retard) position, since the spring inside the vacuum advance would park the linkage all the way to the left when no vacuum is applied.

When the engine is idling, the vacuum port (spark port) on the carburetor is not exposed to engine vacuum, because the drilled hole in the carburetor throat that is connected to the spark port is physically above the throttle butterfly valve. With the throttle butterfly valve fully closed in the idle position, the spark port is isolated from the engine vacuum, which is present in the intake manifold, below the throttle butterfly valve. The centrifugal advance specifications for your distributor indicate that the centrifugal advance would not begin to engage below 800 RPM.

I can only imagine that the static, base timing setting of 18° BTDC (that you established at 500 RPM idle with the vacuum advance hose disconnected from the distributor and plugged) might have been disturbed by the process of disconnecting and reconnecting the vacuum hose to the distributor. This might have occurred if the nut that secures the base of the distributor was not tightened sufficiently. The pressure applied to the vacuum advance mechanism when you reconnected the vacuum tube might have disturbed the distributor setting slightly to change the timing by 2°. Another possibility might be that the vacuum advance mechanism is sticking slightly. If you reconnected the vacuum hose and revved the engine with the hose connected the vacuum advance mechanism would have been actuated momentarily before it moved back to the park position. If the mechanism is sticking slightly or if the breaker plate pivot point is worn, producing a sloppy pivot mechanism, the parked timing position when the vacuum advance mechanism is not active might vary one or two degrees each time the vacuum advance mechanism is relaxed. The possibility of a worn centrifugal advance mechanism in the aging distributor might also introduce several degrees of variation each time the engine is revved, since both the vacuum advance and centrifugal advance have an impact on the timing and may possibly not be returning to the original starting point if there is wear in the distributor mechanism itself.

You may wish to reset the base timing setting with the vacuum advance disconnected one more time. When finished be sure to fully tighten the nut that secures the distributor, and then confirm that the timing setting has not changed. Then reconnect the vacuum advance and rev the engine several times — enough to trigger both the vacuum advance and centrifugal advance mechanisms. Then recheck the base timing with the timing light to confirm that the idle setting has not changed. If the distributor position was accidentally bumped slightly when you reconnected the hose earlier, and if re-tightening the distributor has properly secured it, the static base timing setting should stay the same each time it is rechecked. If the timing variation is occurring because of wear in the distributor mechanism, you may see the base timing will change randomly after you rev the engine and rechecked the timing.

Image
The Engine ID indicates that the engine is a 1965/66 140 hp Manual Transmission engine.

Vacuum Advance Mechanism.jpg
1965 Corvair Chassis Shop Manual Distributor Specifications.jpg
1965 Engine Tune Up Chart.jpg
Brad Bodie
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Re: Timing question

Unread post by 66corsaguy » Fri Sep 22, 2017 3:48 pm

bbodie52 wrote:
66corsaguy wrote:1966 Corsa
I want to make sure I understand correctly about timing for my car

My RPM is at 500 and I set timing to 18 after I unplugged and cinched the vacuum tube.

When I attached tube it went down to 16

Is that normal?

There's talk about total timing is that in reference to when you add throttle and RPM goes up advance moves forward and stops somewhere. (It's off the number chart so I don't know what it's at) is that what total advance is?
I want to make sure I set timing correctly but it dropping down to 16 this may be also be because it warmed up?
The illustrations that I posted below were intended to help illustrate the vacuum advance mechanism, the 140 hp distributor centrifugal and vacuum advance specifications, and the tuneup specifications for your engine. The engine suffix code indicates that it is a 140 hp engine from a 1965-66 Corvair Corsa.

The vacuum advance mechanism moves the breaker plate and ignition points to the right when the vacuum pull is great enough to actuate the vacuum advance. Since the distributor cam rotation his clockwise, moving the points to the right would advance the point where the rubbing block on the ignition points comes into contact with the raised lobe on the distributor cam. The vacuum advance mechanism is normally parked all the way to the left. It would only move to the right when sufficient vacuum was applied to the diaphragm in the vacuum advance mechanism to begin the programmed timing advance. According to the chart the maximum timing advance that would be introduced by the vacuum advance mechanism would be 22° at 14 inches of vacuum. The vacuum advance mechanism cannot normally move the timing associated with location of the breaker plate to the left (retard) position, since the spring inside the vacuum advance would park the linkage all the way to the left when no vacuum is applied.

When the engine is idling, the vacuum port (spark port) on the carburetor is not exposed to engine vacuum, because the drilled hole in the carburetor throat that is connected to the spark port is physically above the throttle butterfly valve. With the throttle butterfly valve fully closed in the idle position, the spark port is isolated from the engine vacuum, which is present in the intake manifold, below the throttle butterfly valve. The centrifugal advance specifications for your distributor indicate that the centrifugal advance would not begin to engage below 800 RPM.

I can only imagine that the static, base timing setting of 18° BTDC (that you established at 500 RPM idle with the vacuum advance hose disconnected from the distributor and plugged) might have been disturbed by the process of disconnecting and reconnecting the vacuum hose to the distributor. This might have occurred if the nut that secures the base of the distributor was not tightened sufficiently. The pressure applied to the vacuum advance mechanism when you reconnected the vacuum tube might have disturbed the distributor setting slightly to change the timing by 2°. Another possibility might be that the vacuum advance mechanism is sticking slightly. If you reconnected the vacuum hose and revved the engine with the hose connected the vacuum advance mechanism would have been actuated momentarily before it moved back to the park position. If the mechanism is sticking slightly or if the breaker plate pivot point is worn, producing a sloppy pivot mechanism, the parked timing position when the vacuum advance mechanism is not active might vary one or two degrees each time the vacuum advance mechanism is relaxed. The possibility of a worn centrifugal advance mechanism in the aging distributor might also introduce several degrees of variation each time the engine is revved, since both the vacuum advance and centrifugal advance have an impact on the timing and may possibly not be returning to the original starting point if there is wear in the distributor mechanism itself.

You may wish to reset the base timing setting with the vacuum advance disconnected one more time. When finished be sure to fully tighten the nut that secures the distributor, and then confirm that the timing setting has not changed. Then reconnect the vacuum advance and rev the engine several times — enough to trigger both the vacuum advance and centrifugal advance mechanisms. Then recheck the base timing with the timing light to confirm that the idle setting has not changed. If the distributor position was accidentally bumped slightly when you reconnected the hose earlier, and if re-tightening the distributor has properly secured it, the static base timing setting should stay the same each time it is rechecked. If the timing variation is occurring because of wear in the distributor mechanism, you may see the base timing will change randomly after you rev the engine and rechecked the timing.

Image
The Engine ID indicates that the engine is a 1965/66 140 hp Manual Transmission engine.

Vacuum Advance Mechanism.jpg
1965 Corvair Chassis Shop Manual Distributor Specifications.jpg
1965 Engine Tune Up Chart.jpg
Ok. I am going to set my timing again. I should raise idle to 650 and than set timing between 16-20 based on how it runs



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Re: Timing question

Unread post by 66corsaguy » Fri Sep 22, 2017 3:49 pm

terribleted wrote:500 rpm is a bit low..isn't the spec 600 (check the manual). Generally the timing at idle will not go down when connecting the plugged vacuum line it should not really change. (it was plugged when you set the timing wasn't it? (again check the manual it should be removed and plugged). Is it a turbo? If that's the case timing at 16 is way low should be 24 degrees and idle at 850....if it is a turbo the rpm might drop when the vacuum retard is connected if it is active. It should not be active at idle. If it is a 140 then idle RPM should be 600-650 and timing between 16 and 20 before tdc. I find most 140's like near 20. Re-read the chart on page 6-2 of the 65 primary book shop manual for guidance.
Ok. I'm going to do again and raise idle


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Re: Timing question

Unread post by 66corsaguy » Fri Sep 22, 2017 4:06 pm

I am trying to adjust my idle and am I supposed bend the ting or turn the screw. Turning the screw doesn't seem to do anything. I am finding when the car is fully warmed up the idle is too low and it wants to stall and rattle everything.


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Re: Timing question

Unread post by bbodie52 » Fri Sep 22, 2017 5:55 pm

You do not bend any portion of the carburetor linkage to adjust the idle speed. The idle speed screws and idle mixture screws out the only point of adjustment. The cross-linkage that connects the left and right primary carburetors together, and the linkage that ties the cross-link age to the accelerator pedal can all have an impact on the idle adjustment of each primary carburetor. The shop manual carburetor adjustment procedure (outlined in the two videos below) starts with disconnecting the cross-linkage from each primary carburetor, so that the two carburetors are isolated from each other and not affected by the portion of the linkage that ties them together and connects them to the accelerator pedal. With the carburetors isolated, a strip of paper is used like a feeler gauge between the idle speed screw and the carburetor linkage, so that you can feel when the screw has been backed out enough to just release tension on the paper. This establishes the zero contact point between the screw and the carburetor linkage. The screw is then tightened 1½ turns to establish an initial idle setting for each carburetor that is mechanically synchronized with the other primary carburetor. Any further adjustments to these two screws should be made equally on both sides, to keep the mechanically in sync. The idle mixture screws are also synchronized by turning them clockwise until they bottom out in the carburetor and then backing them out 1½ turns each. This establishes an equal mechanical items mixture setting on each primary carburetor.

I would recommend reviewing this procedure in the attached tuneup section of the shop manual and taking a few minutes to watch the two videos below. This should help to establish clearly in your mind the objective of synchronizing the two primary carburetors and keeping the same adjustments on both. The cross linkage is not reconnected until you are finished synchronizing the carburetors and establishing the final idle speed setting. The right carburetor is then connected to the cross linkage, and then the left side (which is adjustable) is turned so that it slipped into the cross linkage without changing the pressure on either carburetor. The final step involves reconnecting the portion of the linkage that ties to the accelerator pedal.

Image

Tuning the Corvair Engine — Part 1



Tuning The Corvair Engine — Part 2



The following section describes the use of a UniSyn gauge to synchronize the carburetors. It is more accurate than a mechanical adjustment because it actually measures airflow through each carburetor and allows you to synchronize them based on this instrument measurement rather than a simple mechanical adjustment that assumes that both carburetors are flowing equally based on simple mechanical settings. The UniSyn gauge has been around since the 1950s and is often used to synchronize multiple carburetors in automobiles and motorcycles. Its use was often described in Corvair articles in the 1960s. I would suggest that you read the following material and then decide if you would like to add a UniSyn gauge to your toolbox.
bbodie52 wrote:
flat6_musik wrote:...I bought a Uni-Syn and only used it once. It seemed to me that at idle, there was barely enough air flow to raise the ball. It pissed me off and I put it away...
The Uni-Syn Carburetor Balancing Instrument is a tool that I remember as far back as the 1950s and 1960s. It was designed for use in multi-carburetor automobiles, motorcycles, etc. that were initially common in European vehicles, but were later found in American vehicles like the Corvair.
Image :confused:
:idea: The Uni-Syn is an airflow gauge that must be calibrated to match the specific engine airflow moving through the carburetor throat. The flow control in the center of the Uni-Syn is mounted on a threaded pin. Rotating the flow control raises or lowers it, which increases/decreases the air gap, which impacts the air velocity passing the oriface that allows some airflow to pass through the gauge. With the Uni-Syn held firmly on the carburetor intake with the engine idling, the flow control is adjusted so that the plastic float is approximately centered in the glass sight tube. Once calibrated, the Uni-Syn can be moved back and forth between the two primary carburetors to compare airflow at idle. The goal is to play with the idle speed screws to get an even airflow level that matches between both carburetors, and at the same time produces the desired idle speed. Before fine-tuning this idle balance with a Uni-Syn, the ignition system, idle speed and idle mixture should have been adjusted following the standard procedures as described in the factory shop manual. The balancing step with the Uni-Syn gauge is added at the end of the tuning procedure to measure actual airflow though both carburetors at idle, and balancing that airflow using the airflow meter as a measuring tool, rather than simply relying on a physical balanced "calibration" using a strip of paper to detect initial contact between the idle speed adjustment screws and the carburetor linkage, followed by counting the screw turns needed to obtain the desired idle speed (and ensuring that the same number of screw turns are applied to each screw). That procedure achieves a fairly close initial setup. The use of the Uni-Syn airflow gauge as a final step ensures balance between the two carburetors by measuring actual airflow.

:wrench: Once the balanced idle airflow and desired idle speed have been achieved, a similar procedure can be used to synchronize the airflow when the carburetors are held open at a faster engine speed by the throttle linkage. Again, the shop manual procedure can be used to set the initial mechanical balance between the two sides of the throttle linkage. The linkage segment connecting the accelerator pedal to the cross-linkage between the two carburetors is temporarily disconnected, and a turnbuckle is temporarily attached to hold the throttle opened against the pull of the throttle return spring.
Image
The turnbuckle can be adjusted to hold the throttle open at approximately 1500 RPM. The Uni-Syn center flow control is readjusted to re-calibrate the float to a position somewhere in the center travel of the sight tube, based on the increased airflow through the carburetors at the higher steady RPM maintained by the turnbuckle arrangement. As with the idle synchronization procedure, the re-calibrated Uni-Syn is used to measure the airflow moving through the two carburetors. The goal is to fine-tune the threaded portion of the carburetor actuation linkage so that the same airflow reading is attained on each carburetor, but this time with the throttles held open by a pull on the throttle linkage, instead of by the setting of the idle speed screws. When the airflow has been balanced using the throttle linkage adjustment, the balancing procedure has been completed and the normal accelerator pedal throttle linkage can be reconnected.

Image
TIPS & CLARIFICATION...

With the engine at idle, you want to open the Uni-Syn flow control as much as possible, but still keep the float in the sight glass at about mid-level. Then check the other carburetor, which you want to read the same flow rate. You may have to adjust the flow control a few times as you adjust the carburetor settings. Just remember to check each carburetor with the flow control set at the same point, and to keep the sight glass in the vertical to prevent the float from hanging up in the tube.

The wheel in the Uni-Syn venturi controls the flow through the tube, or in other words how high the bead is in the cylinder for a given engine speed. You need enough flow to not strangle the engine, and the bead works just as well in the lower third (which still lets good air flow through). Make sure the idle speed doesn't drop when you place the tool on the carb: if it does, open it up.

Before setting the carbs, make sure that the ignition is right: points and timing set, good wires and plugs. Rich running is often blamed on carbs when in fact it's a weak, retarded spark. Check the throttle shafts: loose ones let in air and lean the mixture, raising idle speed, as well as throw off the linkage action. Check the linkage that connects the carburetors. if it's loose, one will open before the other. Make sure there are no vacuum leaks.

With a twin carburetor set up, disconnect the linkage that connects one carburetor to the other. Set the idle speed with the linkage screws first. Use the Uni-Syn to check that each carburetor is drawing equally at idle. This may take a few tries until you get both drawing equally at the speed you want. Blip the throttle to see if they come back to those settings (worn throttle shafts can fool you). Set the idle mixture screws in accordance with the shop manual instructions. Check the balance again. Hook the linkage back up. If one carburetor now draws more, adjust the linkage until it's back to roughly equal.

Once the carburetors are drawing equally at idle, hold an engine speed: at about 1500 RPM. This checks that the mechanical linkage is pulling equally. You'll need to open up the Uni-Syn center wheel to draw more air and bring the bead down in the tube. If both carburetors are within a bead's thickness of each other, that's good. If one is definitely off from the other, the higher flow carburetor's linkage is being pulled more than the other. You'll need to figure out why that's happening mechanically to rectify it. :chevy:
Attachments
1965 Corvair Chassis Shop Manual - SECTION 6 - ENGINE TUNE-UP.pdf
1965 Corvair Chassis Shop Manual - SECTION 6 - ENGINE TUNE-UP
(2.92 MiB) Downloaded 2 times
DELCO ROCHESTER - Models H, HV Carburetor Service Manual.pdf
DELCO ROCHESTER - Models H, HV Carburetor Service Manual
(1.79 MiB) Downloaded 3 times
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible

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Re: Timing question

Unread post by terribleted » Fri Sep 22, 2017 6:42 pm

66corsaguy wrote:
Fri Sep 22, 2017 4:06 pm
I am trying to adjust my idle and am I supposed bend the ting or turn the screw. Turning the screw doesn't seem to do anything. I am finding when the car is fully warmed up the idle is too low and it wants to stall and rattle everything.


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Do neither right nor left idle speed screws effect the idle? Look for major vacuum leaks and eliminate. Suspect that the carbs are it poor condition or very badly adjusted. If adjusting the idle speed screws has no effect generally that carb is messed. Dissassemble, clean and properly adjust the carbs, then try again.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
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Re: Timing question

Unread post by 66corsaguy » Fri Sep 22, 2017 8:13 pm

terribleted wrote:
66corsaguy wrote:
Fri Sep 22, 2017 4:06 pm
I am trying to adjust my idle and am I supposed bend the ting or turn the screw. Turning the screw doesn't seem to do anything. I am finding when the car is fully warmed up the idle is too low and it wants to stall and rattle everything.


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Do neither right nor left idle speed screws effect the idle? Look for major vacuum leaks and eliminate. Suspect that the carbs are it poor condition or very badly adjusted. If adjusting the idle speed screws has no effect generally that carb is messed. Dissassemble, clean and properly adjust the carbs, then try again.
Rebuilt the carbs so I am confident They are clean BUT I had to block off my secondary carbs (capped fuel line) because of a fuel leak. I have not bought the plates so there very may well be air leaking thru the throttle plate although I did seal them they certainly may still be leaking especially since I suspect worn throttle bar (leaking there)

Ok I will fix the leaking carbs or buy the plates from clarks. Gosh darn it. I just want to drive!!!


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Re: Timing question

Unread post by 66corsaguy » Fri Sep 22, 2017 8:21 pm

bbodie52 wrote:You do not bend any portion of the carburetor linkage to adjust the idle speed. The idle speed screws and idle mixture screws out the only point of adjustment. The cross-linkage that connects the left and right primary carburetors together, and the linkage that ties the cross-link age to the accelerator pedal can all have an impact on the idle adjustment of each primary carburetor. The shop manual carburetor adjustment procedure (outlined in the two videos below) starts with disconnecting the cross-linkage from each primary carburetor, so that the two carburetors are isolated from each other and not affected by the portion of the linkage that ties them together and connects them to the accelerator pedal. With the carburetors isolated, a strip of paper is used like a feeler gauge between the idle speed screw and the carburetor linkage, so that you can feel when the screw has been backed out enough to just release tension on the paper. This establishes the zero contact point between the screw and the carburetor linkage. The screw is then tightened 1½ turns to establish an initial idle setting for each carburetor that is mechanically synchronized with the other primary carburetor. Any further adjustments to these two screws should be made equally on both sides, to keep the mechanically in sync. The idle mixture screws are also synchronized by turning them clockwise until they bottom out in the carburetor and then backing them out 1½ turns each. This establishes an equal mechanical items mixture setting on each primary carburetor.

I would recommend reviewing this procedure in the attached tuneup section of the shop manual and taking a few minutes to watch the two videos below. This should help to establish clearly in your mind the objective of synchronizing the two primary carburetors and keeping the same adjustments on both. The cross linkage is not reconnected until you are finished synchronizing the carburetors and establishing the final idle speed setting. The right carburetor is then connected to the cross linkage, and then the left side (which is adjustable) is turned so that it slipped into the cross linkage without changing the pressure on either carburetor. The final step involves reconnecting the portion of the linkage that ties to the accelerator pedal.

Image

Tuning the Corvair Engine — Part 1



Tuning The Corvair Engine — Part 2



The following section describes the use of a UniSyn gauge to synchronize the carburetors. It is more accurate than a mechanical adjustment because it actually measures airflow through each carburetor and allows you to synchronize them based on this instrument measurement rather than a simple mechanical adjustment that assumes that both carburetors are flowing equally based on simple mechanical settings. The UniSyn gauge has been around since the 1950s and is often used to synchronize multiple carburetors in automobiles and motorcycles. Its use was often described in Corvair articles in the 1960s. I would suggest that you read the following material and then decide if you would like to add a UniSyn gauge to your toolbox.
bbodie52 wrote:
flat6_musik wrote:...I bought a Uni-Syn and only used it once. It seemed to me that at idle, there was barely enough air flow to raise the ball. It pissed me off and I put it away...
The Uni-Syn Carburetor Balancing Instrument is a tool that I remember as far back as the 1950s and 1960s. It was designed for use in multi-carburetor automobiles, motorcycles, etc. that were initially common in European vehicles, but were later found in American vehicles like the Corvair.
Image :confused:
:idea: The Uni-Syn is an airflow gauge that must be calibrated to match the specific engine airflow moving through the carburetor throat. The flow control in the center of the Uni-Syn is mounted on a threaded pin. Rotating the flow control raises or lowers it, which increases/decreases the air gap, which impacts the air velocity passing the oriface that allows some airflow to pass through the gauge. With the Uni-Syn held firmly on the carburetor intake with the engine idling, the flow control is adjusted so that the plastic float is approximately centered in the glass sight tube. Once calibrated, the Uni-Syn can be moved back and forth between the two primary carburetors to compare airflow at idle. The goal is to play with the idle speed screws to get an even airflow level that matches between both carburetors, and at the same time produces the desired idle speed. Before fine-tuning this idle balance with a Uni-Syn, the ignition system, idle speed and idle mixture should have been adjusted following the standard procedures as described in the factory shop manual. The balancing step with the Uni-Syn gauge is added at the end of the tuning procedure to measure actual airflow though both carburetors at idle, and balancing that airflow using the airflow meter as a measuring tool, rather than simply relying on a physical balanced "calibration" using a strip of paper to detect initial contact between the idle speed adjustment screws and the carburetor linkage, followed by counting the screw turns needed to obtain the desired idle speed (and ensuring that the same number of screw turns are applied to each screw). That procedure achieves a fairly close initial setup. The use of the Uni-Syn airflow gauge as a final step ensures balance between the two carburetors by measuring actual airflow.

:wrench: Once the balanced idle airflow and desired idle speed have been achieved, a similar procedure can be used to synchronize the airflow when the carburetors are held open at a faster engine speed by the throttle linkage. Again, the shop manual procedure can be used to set the initial mechanical balance between the two sides of the throttle linkage. The linkage segment connecting the accelerator pedal to the cross-linkage between the two carburetors is temporarily disconnected, and a turnbuckle is temporarily attached to hold the throttle opened against the pull of the throttle return spring.
Image
The turnbuckle can be adjusted to hold the throttle open at approximately 1500 RPM. The Uni-Syn center flow control is readjusted to re-calibrate the float to a position somewhere in the center travel of the sight tube, based on the increased airflow through the carburetors at the higher steady RPM maintained by the turnbuckle arrangement. As with the idle synchronization procedure, the re-calibrated Uni-Syn is used to measure the airflow moving through the two carburetors. The goal is to fine-tune the threaded portion of the carburetor actuation linkage so that the same airflow reading is attained on each carburetor, but this time with the throttles held open by a pull on the throttle linkage, instead of by the setting of the idle speed screws. When the airflow has been balanced using the throttle linkage adjustment, the balancing procedure has been completed and the normal accelerator pedal throttle linkage can be reconnected.

Image
TIPS & CLARIFICATION...

With the engine at idle, you want to open the Uni-Syn flow control as much as possible, but still keep the float in the sight glass at about mid-level. Then check the other carburetor, which you want to read the same flow rate. You may have to adjust the flow control a few times as you adjust the carburetor settings. Just remember to check each carburetor with the flow control set at the same point, and to keep the sight glass in the vertical to prevent the float from hanging up in the tube.

The wheel in the Uni-Syn venturi controls the flow through the tube, or in other words how high the bead is in the cylinder for a given engine speed. You need enough flow to not strangle the engine, and the bead works just as well in the lower third (which still lets good air flow through). Make sure the idle speed doesn't drop when you place the tool on the carb: if it does, open it up.

Before setting the carbs, make sure that the ignition is right: points and timing set, good wires and plugs. Rich running is often blamed on carbs when in fact it's a weak, retarded spark. Check the throttle shafts: loose ones let in air and lean the mixture, raising idle speed, as well as throw off the linkage action. Check the linkage that connects the carburetors. if it's loose, one will open before the other. Make sure there are no vacuum leaks.

With a twin carburetor set up, disconnect the linkage that connects one carburetor to the other. Set the idle speed with the linkage screws first. Use the Uni-Syn to check that each carburetor is drawing equally at idle. This may take a few tries until you get both drawing equally at the speed you want. Blip the throttle to see if they come back to those settings (worn throttle shafts can fool you). Set the idle mixture screws in accordance with the shop manual instructions. Check the balance again. Hook the linkage back up. If one carburetor now draws more, adjust the linkage until it's back to roughly equal.

Once the carburetors are drawing equally at idle, hold an engine speed: at about 1500 RPM. This checks that the mechanical linkage is pulling equally. You'll need to open up the Uni-Syn center wheel to draw more air and bring the bead down in the tube. If both carburetors are within a bead's thickness of each other, that's good. If one is definitely off from the other, the higher flow carburetor's linkage is being pulled more than the other. You'll need to figure out why that's happening mechanically to rectify it. :chevy:
I have all the manuals and have read them over and over and than I have books from authors and than I read the forums. Unfortunately some book information does contrast with the manual.
About bending the tang : In bob helts book he states to bend the tang see photo of text Image

So it can be a little confusing.


Also I thought I read that I am to set idle and timing before balancing the carbs with the unisync. I have them screwed out I think 1 1/2 turns to start.




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66corsaguy
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Re: Timing question

Unread post by 66corsaguy » Fri Sep 22, 2017 8:24 pm

66corsaguy wrote:
bbodie52 wrote:You do not end any portion of the carburetor linkage to adjust the idle speed. The idle speed screws and idle mixture screws out the only point of adjustment. The cross-linkage that connects the left and right primary carburetors together, and the linkage that ties the cross-link age to the accelerator pedal can all have an impact on the idle adjustment of each primary carburetor. The shop manual carburetor adjustment procedure (outlined in the two videos below) starts with disconnecting the cross-linkage from each primary carburetor, so that the two carburetors are isolated from each other and not affected by the portion of the linkage that ties them together and connects them to the accelerator pedal. With the carburetors isolated, a strip of paper is used like a feeler gauge between the idle speed screw and the carburetor linkage, so that you can feel when the screw has been backed out enough to just release tension on the paper. This establishes the zero contact point between the screw and the carburetor linkage. The screw is then tightened 1½ turns to establish an initial idle setting for each carburetor that is mechanically synchronized with the other primary carburetor. Any further adjustments to these two screws should be made equally on both sides, to keep the mechanically in sync. The idle mixture screws are also synchronized by turning them clockwise until they bottom out in the carburetor and then backing them out 1½ turns each. This establishes an equal mechanical items mixture setting on each primary carburetor.

I would recommend reviewing this procedure in the attached tuneup section of the shop manual and taking a few minutes to watch the two videos below. This should help to establish clearly in your mind the objective of synchronizing the two primary carburetors and keeping the same adjustments on both. The cross linkage is not reconnected until you are finished synchronizing the carburetors and establishing the final idle speed setting. The right carburetor is then connected to the cross linkage, and then the left side (which is adjustable) is turned so that it slipped into the cross linkage without changing the pressure on either carburetor. The final step involves reconnecting the portion of the linkage that ties to the accelerator pedal.

Image

Tuning the Corvair Engine — Part 1



Tuning The Corvair Engine — Part 2



The following section describes the use of a UniSyn gauge to synchronize the carburetors. It is more accurate than a mechanical adjustment because it actually measures airflow through each carburetor and allows you to synchronize them based on this instrument measurement rather than a simple mechanical adjustment that assumes that both carburetors are flowing equally based on simple mechanical settings. The UniSyn gauge has been around since the 1950s and is often used to synchronize multiple carburetors in automobiles and motorcycles. Its use was often described in Corvair articles in the 1960s. I would suggest that you read the following material and then decide if you would like to add a UniSyn gauge to your toolbox.
bbodie52 wrote: The Uni-Syn Carburetor Balancing Instrument is a tool that I remember as far back as the 1950s and 1960s. It was designed for use in multi-carburetor automobiles, motorcycles, etc. that were initially common in European vehicles, but were later found in American vehicles like the Corvair.
Image :confused:
:idea: The Uni-Syn is an airflow gauge that must be calibrated to match the specific engine airflow moving through the carburetor throat. The flow control in the center of the Uni-Syn is mounted on a threaded pin. Rotating the flow control raises or lowers it, which increases/decreases the air gap, which impacts the air velocity passing the oriface that allows some airflow to pass through the gauge. With the Uni-Syn held firmly on the carburetor intake with the engine idling, the flow control is adjusted so that the plastic float is approximately centered in the glass sight tube. Once calibrated, the Uni-Syn can be moved back and forth between the two primary carburetors to compare airflow at idle. The goal is to play with the idle speed screws to get an even airflow level that matches between both carburetors, and at the same time produces the desired idle speed. Before fine-tuning this idle balance with a Uni-Syn, the ignition system, idle speed and idle mixture should have been adjusted following the standard procedures as described in the factory shop manual. The balancing step with the Uni-Syn gauge is added at the end of the tuning procedure to measure actual airflow though both carburetors at idle, and balancing that airflow using the airflow meter as a measuring tool, rather than simply relying on a physical balanced "calibration" using a strip of paper to detect initial contact between the idle speed adjustment screws and the carburetor linkage, followed by counting the screw turns needed to obtain the desired idle speed (and ensuring that the same number of screw turns are applied to each screw). That procedure achieves a fairly close initial setup. The use of the Uni-Syn airflow gauge as a final step ensures balance between the two carburetors by measuring actual airflow.

:wrench: Once the balanced idle airflow and desired idle speed have been achieved, a similar procedure can be used to synchronize the airflow when the carburetors are held open at a faster engine speed by the throttle linkage. Again, the shop manual procedure can be used to set the initial mechanical balance between the two sides of the throttle linkage. The linkage segment connecting the accelerator pedal to the cross-linkage between the two carburetors is temporarily disconnected, and a turnbuckle is temporarily attached to hold the throttle opened against the pull of the throttle return spring.
Image
The turnbuckle can be adjusted to hold the throttle open at approximately 1500 RPM. The Uni-Syn center flow control is readjusted to re-calibrate the float to a position somewhere in the center travel of the sight tube, based on the increased airflow through the carburetors at the higher steady RPM maintained by the turnbuckle arrangement. As with the idle synchronization procedure, the re-calibrated Uni-Syn is used to measure the airflow moving through the two carburetors. The goal is to fine-tune the threaded portion of the carburetor actuation linkage so that the same airflow reading is attained on each carburetor, but this time with the throttles held open by a pull on the throttle linkage, instead of by the setting of the idle speed screws. When the airflow has been balanced using the throttle linkage adjustment, the balancing procedure has been completed and the normal accelerator pedal throttle linkage can be reconnected.

Image
TIPS & CLARIFICATION...

With the engine at idle, you want to open the Uni-Syn flow control as much as possible, but still keep the float in the sight glass at about mid-level. Then check the other carburetor, which you want to read the same flow rate. You may have to adjust the flow control a few times as you adjust the carburetor settings. Just remember to check each carburetor with the flow control set at the same point, and to keep the sight glass in the vertical to prevent the float from hanging up in the tube.

The wheel in the Uni-Syn venturi controls the flow through the tube, or in other words how high the bead is in the cylinder for a given engine speed. You need enough flow to not strangle the engine, and the bead works just as well in the lower third (which still lets good air flow through). Make sure the idle speed doesn't drop when you place the tool on the carb: if it does, open it up.

Before setting the carbs, make sure that the ignition is right: points and timing set, good wires and plugs. Rich running is often blamed on carbs when in fact it's a weak, retarded spark. Check the throttle shafts: loose ones let in air and lean the mixture, raising idle speed, as well as throw off the linkage action. Check the linkage that connects the carburetors. if it's loose, one will open before the other. Make sure there are no vacuum leaks.

With a twin carburetor set up, disconnect the linkage that connects one carburetor to the other. Set the idle speed with the linkage screws first. Use the Uni-Syn to check that each carburetor is drawing equally at idle. This may take a few tries until you get both drawing equally at the speed you want. Blip the throttle to see if they come back to those settings (worn throttle shafts can fool you). Set the idle mixture screws in accordance with the shop manual instructions. Check the balance again. Hook the linkage back up. If one carburetor now draws more, adjust the linkage until it's back to roughly equal.

Once the carburetors are drawing equally at idle, hold an engine speed: at about 1500 RPM. This checks that the mechanical linkage is pulling equally. You'll need to open up the Uni-Syn center wheel to draw more air and bring the bead down in the tube. If both carburetors are within a bead's thickness of each other, that's good. If one is definitely off from the other, the higher flow carburetor's linkage is being pulled more than the other. You'll need to figure out why that's happening mechanically to rectify it. :chevy:
I have all the manuals and have read them over and over and than I have books from authors and than I read the forums. Unfortunately some book information does contrast with the manual.
About bending the tang : In bob helts book he states to bend the tang see photo of text Image

So it can be a little confusing.


Also I thought I read that I am to set idle and timing before balancing the carbs with the unisync. I have them screwed out I think 1 1/2 turns to start.




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I will print out what you've written above and go thru again but I think I have to get the secondaries stabilized. It must be drawing in air as Ted mentioned.


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Re: Timing question

Unread post by bbodie52 » Sat Sep 23, 2017 6:18 am

I have all the manuals and have read them over and over and than I have books from authors and than I read the forums. Unfortunately some book information does contrast with the manual.

About bending the tang : In bob helts book he states to bend the tang see photo of text Image
Image
So it can be a little confusing.

Also I thought I read that I am to set idle and timing before balancing the carbs with the unisync. I have them screwed out I think 1 1/2 turns to start.
:doh: :dontknow: :think: You are right — it can be confusing if you do not understand the objective of the procedure that is being discussed. In the case of this book illustration, the procedure for bending the tang has nothing to do with setting the base idle speed. The procedure discussed would be used for modifying or adjusting the FAST IDLE SPEED that is associated with the choke mechanism. The procedure you described in the section of Bob Helt's book is applicable to adjusting the choke mechanism, which only impacts the engine idle when the engine is cold. Once the engine warms to normal operating temperatures the choke mechanism would be fully disengaged and will have no impact on normal engine operation.

Tuning the engine, including setting the base ignition system dwell and timing, idle speed, and synchronizing the carburetors are all intended to be done with the engine at normal operating temperatures and the choke mechanism disengaged. If you are trying to adjust the idle speed before the engine has fully warmed up, and when the carburetor throttle linkage has still engaged the choke mechanism fast idle cam you would be unsuccessful.

There is definitely an interaction between the various subsystems in the ignition system and fuel system. It is important to follow the tuning procedures and do them sequentially in the right order to obtain a good outcome. For example, if your distributor uses ignition points, changing the point gap (dwell) does affect the ignition timing. You would not wish to adjust the ignition timing first before you adjust the point gap. By the same token, changing the ignition timing can affect the idle speed. You would not expect to be able to attain a final idle speed if you had to adjust the ignition timing afterward. However, it is important to understand the impact of the vacuum advance and centrifugal advance on idle speed and timing. If your idle speed is so fast (greater than 800 RPM) that the centrifugal advance comes into play, the engine is idling too fast to accurately set the base ignition timing. Likewise, if the vacuum advance hose is connected and the idle speed screw on the right carburetor has been adjusted to a point where the throttle butterfly valve is opened too far, enough intake manifold vacuum may reach the spark port on the carburetor to cause the vacuum advance to advance the timing. Again, the idle setting on the right carburetor and the connection of the vacuum advance hose would make it impossible to set the timing accurately with the timing light. Some of the basic settings for the carburetors are done with the engine not running. The procedure that is described using a strip of paper to feel the point at which the idle speed screw just comes into contact with the carburetor throttle linkage is done with the engine not running and with the choke mechanism temporarily disconnected to ensure that the fast idle cam is not engaged. This initial idle speed and idle mixture screw setting on each carburetor provides an identical mechanical adjustment to be used as a starting point for tuning the engine. It is accomplished with both the choke mechanism and the cross linkage between the two carburetors disconnected. Once these basic carburetor settings have been established, the ignition points would also be set with a feeler gauge. The engine would be started and warm to full operating temperature. The ignition point dwell would be checked with a dwell tachometer. If the points needed to be adjusted because the dwell reading was out of spec, this would be accomplished before proceeding with adjusting the timing. With the points properly adjusted the engine is restarted, and with the vacuum advance disconnected and plugged the idle speed would be confirmed to be low enough to prevent the centrifugal advance from being engaged. If the idle speed was greater than 800 RPM the idle speed screws would be backed off equally on both carburetors to lower the RPM below 800 RPM. Then the timing light would be used to check the base ignition timing. Once the timing and dwell had been improperly adjusted it is possible to proceed with establishing a proper idle speed — making any adjustments equally on both sides to keep both primary carburetors and mechanical sync. If you are using a UniSyn gauge, the tachometer and UniSyn gauge would be used simultaneously as a final step to ensure that airflow through each primary carburetor is matched and in sync and that the final idle speed is attained by fine-tuning the idle speed and idle mixture screws in conjunction with the tachometer readings and the UniSyn gauge readings. It is often necessary to go back and forth with the carburetor adjustments while watching the instruments to obtain a final goal of having the engine at the proper idle speed and also having the carburetors synchronized. Once the carburetors have been synchronized the cross linkage is reconnected — using the linkage on the left carburetor (which includes a screw adjustment) to reattach the cross linkage to both carburetors without impacting the idle speed. Once this is been done the portion of the linkage that connects to the throttle pedal is adjusted so that it engages with the linkage without impacting the idle speed.

All of the steps require an understanding of the goals involved and an understanding of the potential for impact between one setting and another.

The book that I attached earlier, DELCO ROCHESTER - Models H, HV Carburetor Service Manual contains a lot of information describing the functional operation of each carburetor subsystem. The 1960s vintage ignition and carburetor systems accomplish many of the engine control functions that present day electronic computer programmed systems perform with electronic sensors and preprogrammed engine operating parameters. But they do it without the benefit of electronic sensors and electronic control circuits. Instead, they use mechanical weights and springs and vacuum diaphragms and integrated vacuum ports and other mechanical mechanisms within the carburetor to accomplish what we use electronic fuel injection and electronic ignition control to perform now. Though the 1960s carburetors and ignition systems were not as sophisticated as modern electronic systems are, they did manage to do a fairly good job of controlling engine operation through a wide variety of engine speeds, performance and throttle settings, and operating environment changes. The Corvair mechanic must make many adjustments that impact engine operation. These adjustments would not be necessary on a modern engine since electronic sensors and preprogrammed electronic computer control keeps the engine operating as design engineers intended. Bob Helt's book and the Delco Rochester service manual contain enough theory information to help the mechanic to understand the purpose of the various settings and adjustments that must be made in the fuel system to attain proper engine operation. As described in the tuneup videos, it is essential to have an understanding of the sequence and need for each adjustment to accomplish the final goal of an engine that runs properly and reliably. Performing these adjustments out of order or improperly adjusting one setting to compensate for a faulty adjustment somewhere else often ends with frustration and confusion when the engine fails to perform as desired.
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Re: Timing question

Unread post by tom becker » Sat Sep 23, 2017 8:02 am

If your engine is not a turbo, I would check the advance weights in the distributor. I was having problems trying to find out why the engine ran poorly. After several months I tore the distributor apart only to find the advance weights were put in backwards. This caused the timing to retard as the engine revved up not advance. After fixing the problem and car ran great. Not sure if any of this has anything to do with your problem. TOM

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Re: Timing question

Unread post by terribleted » Sat Sep 23, 2017 9:05 am

Concerning the secondary carbs, the key is that the throttle plates must be fully closed. If the plates seal well in the bores of the carbs and are closed all the way they should not present an issue. If you have had the throttle plates out of the carbs make sure they are installed correctly as in evenly touching the carb throats and not upside down. (the plates are beveled so they present a larger contact area on the carb bore. The bevel on the upper side of the plate should be down and should be up on the part of the plate below the throttle shaft. If they are upside down they will be more prone to air leak. ) I would set an initial setting of 2 turns out on the mixture screws on both primaries. Do not touch these again until you have idle and timing set properly. You can then go back and turn the mixture screws in slightly. As soon as the idle changes while you are doing this back out 1/4 turn, set both the same and then do not touch them again:) These generally end up between 1.5 and 2 turns out. Both carbs should have similar idle screw settings once timing and curb idle are in range. If not (one carb speed screw turned way in and the other not for example) there is something wrong in the carbs generally the one that is turned in much farther. Balancing the carbs is to get the airflow at idle the same on each side. The difference in physical idle screw settings between the sides should be small. Balancing should be done after the car is idling warm at the desired setting and timing is correct.
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