Idling issues

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jmikulec
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Idling issues

Post by jmikulec »

65 110 hp
I am having high idling issues when in neutral. There seems to be a large gap between rpm when I go from neutral to drive in the powerglide. What could be wrong?


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terribleted
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Re: Idling issues

Post by terribleted »

Do you have the idle adjusted as slow as it will go without stalling with the car in drive?
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Re: Idling issues

Post by bbodie52 »

jmikulec wrote:Sat Mar 12, 2016 6:39 pm

I have a 65 monza 110 with the powerglide...
Here are a few things that I would look at to begin with, based on the symptoms you describe…

Recheck the static (base) ignition timing with the timing light. (12-16° BTDC) Make sure your vacuum advance is disconnected and plugged when making this check. Also verify that the timing is being set with the idle speed (in neutral) around 600-700 RPM. (If you try to adjust the base ignition timing with the idle speed greater than this, the centrifugal advance may be engaging. You must disconnect the vacuum advance and lower the idle speed sufficiently to ensure that neither the centrifugal advance nor the vacuum advance have come into play).

Follow the carburetor synchronization procedures in the tuneup section of the shop manual (starting on page ENGINE TUNE-UP 6-5, attached). Basically this includes temporarily disconnecting the throttle linkage from the accelerator pedal linkage (using the spring to apply tension to hold the throttle linkage in a fully closed position). The linkage is also detached temporarily at each carburetor and a slip of paper is used to detect when the idle speed screw first contacts the throttle linkage (you can feel tension released on the strip of paper as you slowly back off the screw). Each screw is then tightened 1 1/2 turns to establish an initial preset that is the same on both carburetors. The adjustable linkage component on the left carburetor is then reattached while ensuring that the link slips easily into the throttle linkage without affecting the opening of the butterfly valve in the carburetor. The end result is that both throttle butterfly valves are held fully closed against each idle speed adjustment screw — with the setting at each screw synchronized so that it is 1 1/2 turns down from initial contact with the carburetor linkage. The idle mixture screws are also turned clockwise until they bottom gently. They are then unscrewed 1 1/2 turns to establish an initial synchronized idle mixture setting at each carburetor.

Carburetor Idle Screws.jpg
Check all vacuum connections as shown in the illustration below. Confirm that there are no cracked, split, or loose vacuum connections that would cause a vacuum leak.

Image

Follow the tuneup procedures in the shop manual to achieve appropriate dwell, initial ignition timing, and idle speed (in neutral). Any idle speed settings or idle mixture settings should be duplicated on both primary carburetors. The final idle speed should be close to the recommended speed for a manual transmission, but also should be high enough to prevent the engine from stalling when the transmission is placed in DRIVE.

If you have access to a UniSyn gauge, use it to achieve final synchronization between the two carburetors. It should be used to synchronize both idle speed and partial throttle speed. It measures airflow volume through each carburetor throat, and is more accurate than the initial settings used to only synchronize the physical idle speed screw settings.
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 (listed on the Clark's Corvair Parts Catalog, page 58), 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 orifice 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 (left primary carburetor) 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:
UNI-SYN Carburetor Balancing Instrument Instructions.pdf
UNI-SYN Carburetor Balancing Instrument Instructions
(56.72 KiB) Downloaded 48 times
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 30 times
Brad Bodie
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Re: Idling issues

Post by 64powerglide »

The high idle in neutral is what it is as long as you have 450-500 in drive at hot idle with the vacuum advance disconnected & plugged or clamped off. There is quite a difference between the two. I set my 64 110 at 500 3 years ago have not touched it since. Cannot remember what it read in neutral but it doesn't matter as long as it doesn't stall out in gear. I'm thinking the neutral idle was around 1,300 hundred. :dontknow: If you're not having any problems with it don't fix it!!!!!!
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Rdhog99
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Re: Idling issues

Post by Rdhog99 »

Idling issues and the 1965 engine you have caught my attention. Have you checked out everything others here have offered here that could cause idling issues? If you have eliminated everything else and are still having an idle issue I would add that the last thing on the list to check is the carburetors internally.

The issue I had was of irregular idling and happened to be with 1965 carbs. In the process of fixing it I found some discrepancies in the carburetors. I found that what I thought was a matched pair of carburetors were in fact not matched when checked out thoroughly.

Here is the experience I had in calibrating the idle circuit on a pair of HV carburetors.
Although I was able to get an improvement with idle quality I would like to hear of any comments others have had. There seems to be a lot to learn about just what is really needed and what the changes are really doing. The following concerns the idle circuit only. I think that the changes I ended up making were probably due to the engine combination I have.

Here is the situation I had:
The poor performance issue consists of idle quality that is not stable. Part throttle was not smooth. The engine would unexpectedly stall at times. Float level changes did not help.
The engine being tuned is a ’63 145 cu in 102hp engine using an Isky 260 cam. The engine idles with about 14 inches of vacuum at 14 degrees BTDC. The Corvair engine had just been completely rebuilt. This engine is in a motorcycle so smooth cool running is important. The cylinder head normal temperature now runs cooler after some changes at around 330-370 degrees in open air with no fan.
https://www.youtube.com/watch?v=44I4_H2D8tE
https://www.youtube.com/watch?v=XMiXMSXGxfU


The carburetor used is P/N 7025023 Year 1965.
After being dissatisfied with the idle and part throttle performance on this Corvair engine I made changes to the idle jets and air bleeds. Mixture was measured with an air fuel ratio gauge AFR (wideband sensor). After the following changes were made a much smoother and cooler running engine resulted. I had installed a sensor port in the left and right exhaust pipe so I could verify that both sides were equal in AFR after changes were completed.
I used Bob Helt’s carburetor identification book and verified all jets were appropriate and air bleeds were matched to the ‘65 carburetor.
With the stock ’65 carburetor the idle was not stable even though the mixture was able to be adjusted to 12.5 to 13.0 AFR. It was found that the idle mixture screws were only about ¼ turn out to obtain this AFR. I suspected that poor fuel emulsion/atomizing may be causing this?

First I tried a smaller idle jet size in an attempt to get idle screw setting closer to 1 ½ turns as was the expected setting range. I soldered and drilled the idle jet to .023 inch (from the original .026). Idle mixture was then set to 12.5 to 13 with idle mixture screws. The mixture screws were now about 1 ¼ turns out. AFR with throttle cracked just above idle was 14-14.5 or so. Idle was improved somewhat but still not completely stable. Off idle was more erratic and not as smooth as it should be.
I noticed in Bob Helt’s book that the HV carburetors in 62-63 used a larger idle bleed. As an experiment I modified the venturi clusters in the 65 carburetors. Per Bob’s HV carburetor identification book the ’63 145cu 102hp engine originally used a .025 idle jet and a .089 bleed.
I changed idle bleed from .076 (stock ’65) to .089 which is the size used on ’63 Carburetor and set the idle jet to .025.
First try with the larger idle air bleed of .089 was with an idle jet of .025. This resulted in needing over 3 turns out of the idle mixture screw (idle was smooth at this setting). Off idle was lean 14.5-15 AFR with some misfire. Next I tried a .026 idle jet size with some improvement.
The final setting was .028 for the idle jet. Idle air bleed was kept at .089. Idle mixture screws ended up being set at about 2 turns out. Idle mixture set at 12.8-13 AFR with off idle running around 13 AFR. The result is a very smooth idle and smooth off idle.

The changes in the idle jet and idle air bleed resulted in very smooth running with temperatures being noticeably lowered. I can see now that verifying that the jets and air bleeds are the proper size is a must for these carburetors. I used small drill bits to measure the jets and air bleeds. I did find the original clusters in my carbs did not match the information in Bob’s carburetor identification book so they were not used. Possibly drilled out by someone in the past? Mismatches are something to check for carefully when rebuilding.

Seeing the information in Bob Helt’s carburetor identification book shows that sometimes small changes were made to carburetors to calibrate them to a particular engine combination.
I am still curious as to why changes were needed to the ’65 carburetors? Why did the ’62-’63 carburetors use a much larger idle air bleed? I see that the ’66 and later carburetors have an additional idle air bleed added to the circuit.
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Re: Idling issues

Post by bbodie52 »

:think: A THEORY…

I seem to remember a problem with another car sometime back where one carburetor was malfunctioning and the other was working properly. The engine was essentially idling on only one improperly adjusted primary carburetor, with the other carburetor contributing nothing. With the engine idling off of only one primary the idle speed setting had been opened excessively to keep the engine idling under load in DRIVE. This adjustment was necessary to keep the engine idling under transmission load, but when the load was removed the idle speed would go much higher! The other primary carburetor was apparently blocked internally with dirty fuel passages that were preventing it from contributing the other three cylinders to a balanced idle speed with the transmission load.

This is why I asked if you had checked the initial settings for the idle speed screws on both carburetors — to see if they were synchronized. It may turn out that one carburetor has been adjusted for a high idle setting to compensate for the lack of participation in the other three cylinders on the other side of the engine. This is easier to detect the dual exhaust system, since one side will be idling with a cold exhaust while the other side is much hotter. With a single exhaust the lack of participation on one side will not be as noticeable.

You might be able to detect that one side of your engine is not idling by disconnecting one plug wire at a time. You may find that disconnecting a plug wire on the active side will make a significant difference in the idle speed or may even cause the engine to stall if the transmission is in DRIVE. If the other carburetor on the other side is not really participating, disconnecting spark plugs on that side may not have a significant impact in the idle speed.

If it does turn out that the carburetors are not synchronized and that the engine is only idling on the fuel/air mixture from one carburetor, it could be that only the idle fuel passages in the "dead" carburetor are clogged. When driving the car both sides may come alive when the engine is operating on main jet fuel passages.

If both carburetors are functioning properly it should be possible to mechanically synchronize the idle settings as described in the shop manual. This should produce a good idle speed with the transmission in neutral, and the engine should not stall when shifted to DRIVE. As described in the shop manual the final idle speed for the Powerglide-based engine should be adjusted for a smooth idle with the transmission in DRIVE. But the engine should not race to a much higher speed when shifted to neutral. If it does, then shifting back to DRIVE would likely cause the car to jerk excessively on the transmission is put in gear. This is not the behavior that would be expected in a properly tuned engine. If you do discover that one side of your engine is not idling properly because of the carburetor problem, it may become necessary to tear down the carburetor and thoroughly clean it by soaking the components in carburetor parts dip, thoroughly rinsing all of the fuel passages, and then blowing them out with compressed air.

-------------------------------------------------

:think: Are you by any chance running in engine that is fitted with a Pertronix II electronic ignition? There has been a problem noted in the past with the Pertronix II where half the cylinders electronically drop out at low idle speeds with a Powerglide transmission. This is apparently not a problem with the original Pertronix I electronic ignition. For this reason the Pertronix II is not recommended for use on the Corvair with a Powerglide transmission. The symptoms you describe could reflect a loss of every other cylinder at slow idle speeds with the transmission engaged in DRIVE. Under these circumstances when the transmission was shifted back to neutral the idle speed might increase just enough to reengage the missing cylinders, which might cause the idle speed in NEUTRAL to race to a much higher rpm.

See the link below for a discussion on this subject in another Corvair Forum thread…

:link: viewtopic.php?t=3996

:link: http://corvaircenter.com/phorum/read.ph ... 251,871267
Brad Bodie
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drss
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Re: Idling issues

Post by drss »

Just a question from me.
By any chance are you using a pertronix 2 electronic ignition?
I had the same issues in my 66 with the 110 pg and I removed that and put the points back in, now its almost seamless between neutral and drive.

Just a thought
Shawn S - Calgary
66 Monza 110 hp pg
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Re: Idling issues

Post by drss »

Sorry Brad, missed your last bit of info that you already covered.

Shawn
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Re: Idling issues

Post by bbodie52 »

:goodpost: No problem! My comment was just a guess that was not based on personal experience, but instead it was based on anecdotal information. Your first-hand experience with a Powerglide-based Corvair coupled with a Pertronix Ignitor II helped to confirm and validate my suspicion, although we still have not yet heard back from " jmikulec" to see if it applies in this instance.
Brad Bodie
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