Low power

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topless65
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Low power

Unread post by topless65 » Wed Sep 13, 2017 3:05 am

I can get my 66 Monza 140 4spd to start right up, idles good. When pressing the gas the motor revs up good. The choke coils work and I think i did ok on carb syncing. Timing seems to be on point. Pertronix 2 and flame thrower 2 are good. Here's the problem. When I go to take off the car barely moves unless I am at almost full throttle. Car makes no power until further up the rpm range. It feels like you are starting in 2nd gear. Problem is also present in reverse. Car doesn't make enough power to drive it up onto car ramps. Secondary carbs do not have the linkages to them installed. Any thoughts as to where to start looking. Thanks in advance.

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Wagon Master
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Re: Low power

Unread post by Wagon Master » Wed Sep 13, 2017 7:09 am

1. Not enough initial ignition timing.
2. Vacuum advance on side of distributor is not functioning.
3. Disconnected secondaries are not completely closed causing a vacuum leak.

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bbodie52
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Re: Low power

Unread post by bbodie52 » Wed Sep 13, 2017 7:38 am

:think:

Here are a few things that I would suggest checking…
topless65 wrote:...Car makes no power until further up the rpm range. It feels like you are starting in 2nd gear. Problem is also present in reverse...
TIMING ADVANCE

Did you check to verify that the vacuum advance mechanism appears to be functioning? The centrifugal advance does not come into play on the 140 hp engine until the rpm reaches 2800 RPM or more. If the vacuum advance is not functioning, it's potential of adding up to 22° of ignition timing will not be available to the engine at lower engine speeds. You should be able to see the vacuum advance mechanism physically move the breaker plate on the distributor as you begin to rev the engine.

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There have been some instances where the distributor had been dismantled and reassembled with the centrifugal advance mechanism flipped upside down — creating a centrifugal retard mechanism. You can verify the action of the centrifugal advance by disconnecting the vacuum advance hose and plugging it. Then observe the timing mark using a timing light and increase the engine speed. You should be able to observe the timing mark moving correctly to add more advance to the ignition timing as the engine RPM increases. I accidentally created a centrifugal retard when I overhauled my first distributor back around 1970. The engine seemed to run fine at idle, but when I test drove the car it felt like I was throwing out an anchor as engine speed increased and power disappeared. Higher engine RPM just made things worse! When I rechecked the ignition timing with a timing light, the base setting was correct. But when I reved the engine I noticed that the timing mark went in the wrong direction! That was when I discovered that it was possible to reinstall the centrifugal advance weights upside down — creating a centrifugal retard mechanism.

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topless65 wrote:...Pertronix 2 and flame thrower 2 are good...
You should confirm that the Pertronix components have been properly installed, and that the source voltage and supplies the high output Pertronix Flame-Thrower II coil and the Pertronix Ignitor II electronic ignition module is a full 12 V DC. This means that the ballast resistor wire (labeled 20 W/R/B in the wiring schematic below) should have been bypassed when the Pertronix upgrade system was installed. If it was not bypassed than the source voltage feeding the coil and electronic ignition system may only be a nominal 7 V DC. Keeping the ballast resistor wire in the circuit cancels much of the advantage of the high output coil and can introduce a malfunctioning electronic module in the distributor by providing it with an inadequate source voltage.

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Also, I would recommend that you carefully check your system to ensure that there are no vacuum leaks that could be introducing a very lean fuel/air mixture that could rob your engine of power.

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Brad Bodie
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64powerglide
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Re: Low power

Unread post by 64powerglide » Wed Sep 13, 2017 8:29 pm

What do you mean by "timing seems to be on point"????????? What does your timing light say???
64Powerglide, Jeff Phillips

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topless65
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Re: Low power

Unread post by topless65 » Wed Sep 13, 2017 9:23 pm

Thanks. This is the info I need to start with. I have an old timing light that isn't adjustable. I estimate base idle to be about 16*. Distributor is adjusted to where engine runs smoothest at idle. The marks on the balancer look like they are lined up. I'll do an actual TDC check and compare. This is the first carb car I've actually messed with. I need to go back to school. I'm used to fuel injection. I'll check over all this hopefully this weekend and get back with results. Thank you again.

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topless65
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Re: Low power

Unread post by topless65 » Mon Sep 25, 2017 7:32 am

Ok. I got back into the garage. First off. Thank you for all of your info. It really pointed me in the right direction. Item number 1, timing was way off. I the end of the market on the block said 12, not 16. Readjusted timing. Item number 2, resistor wire was still connected, bypassed and removed. Secondaries are not leaking and an old school vacuum leak check with propane showed no leaks. Item number 3, bad battery, don't forget the basics, bad battery means low voltage through out. Now car runs better bit still low on power. Hooked up a vacuum gauge to carbs port, all 4, 1 at a time and needle is fluctuating rapidly on both sides of the engine. Looks like valve adjustment is next step. Hopefully not worn valve guides. Going to wait and start with a cold adjustment, then a running adjustment.

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terribleted
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Re: Low power

Unread post by terribleted » Mon Sep 25, 2017 8:42 am

If you have not done so, do a compression test first. If you see variation or bad results it will help tell you where to focus your efforts. This symptom could be caused by a number of things including bent valve, loose or dropped valve seat, 1 dead primary carb among other things, the compression test may tell you whether there is an internal or more external issue.
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bbodie52
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Re: Low power

Unread post by bbodie52 » Mon Sep 25, 2017 9:27 am

topless65 wrote:...Hooked up a vacuum gauge to carbs port, all 4, 1 at a time and needle is fluctuating rapidly on both sides of the engine...
If the secondary carburetors have vacuum ports, they are not true secondary carburetors. Secondaries do not have choke mechanisms, idle circuits, vacuum ports, etc.
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topless65
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Re: Low power

Unread post by topless65 » Mon Sep 25, 2017 1:38 pm

I meant the 4 different ports on the primary carbs (choke ports and vacuum advance ports). Went through and did a compression test all cylinders between 125 and 135. Did a valve adjustment and found several loose. Car ran better but still not right. Just as a wild thought I tool off the rear tires that are on the car and put the stock wheels back on. The "big tires" are 255/60/15 on 8 inch wheels. That made a major difference. A few more tweaks and this convertible will be road ready, just in time for winter.

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terribleted
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Re: Low power

Unread post by terribleted » Mon Sep 25, 2017 2:20 pm

Are you sure both carbs are working? One carb not working right can cause your type issue. Engines running on one primary run pretty darn well they just lack power. Just because the carbs were new or rebuilt yesterday does not mean that today they do not have an issue (pays to double check......ask me how I know:) Idle speed screws should be similar in adjustment (one turned in a lot more than the other indicates a problem). A quick test....with engine idling block each primary carb one at a time with the palm of your hand. Normal is engine slows, roughens and may stall. If there is little or no change when you cover a carb, that carb has an issue. Very small bits of debris can easily make a Corvair carb malfunction. Sometimes when I have found this issue I have been able to clear the condition by holding the engine at about 2500RPM or a bit more and slapping my palm over the offending carb repeatedly blocking it off. I have had these vacuum pulses dislodge blockages.
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bbodie52
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Re: Low power

Unread post by bbodie52 » Mon Sep 25, 2017 3:04 pm

The vertical vacuum port (Spark Port) taps into engine vacuum ABOVE THE THROTTLE BUTTERFLY VALVE. With tje throttle closed (engine idling) it has very little access to engine vacuum.

The horizontal vacuum port taps into engine vacuum BELOW THE THROTTLE BUTTERFLY VALVE. It has direct access to intake manifold vacuum at all times -- even at idle. It is normally connected to the choke vacuum break diaphragm (on 1962-69 normally aspirated Corvairs) so that it pulls the choke butterfly valve partially open as soon as the cold engine is running -- to allow more air to enter the carburetor even when the engine is still below normal operating temperatures and the automatic chokes are still engaged. The choke vacuum break is no longer functional when the engine has warmed up and the automatic chokes are disengaged.
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