Corvair Forum

Sorry, this is a long post but here's the scenario: I drove to a car show 25 miles away. On the highway, I had to be in 3rd gear with the gas pedal 3/4 of the way down almost the whole time just to maintain 55 mph (4 speed 140HP). Head temps were highest I've ever seen (310 degrees; likely 50 degrees higher than that though). Previous to that, there sometimes was a decreasing idle (until it would eventually stall) but regular driving was just fine with full power. Here's what I've done:
-checked and adjusted timing with a timing light (verified @16 degrees)
-timing seemed consistent at idle and it advanced when I revved the engine
-I took the tops off the primaries and checked inside. Main jets weren't clogged, venturi clusters/emulsion tubes/idle jets were fine. Accelerator pumps work great.
-I've raised the idle speed about 1 whole turn
-richened idle mixture about 1/2 turn (that seemed to at least steady the idle)
-swapped ignition coils (I already mounted it on the vertical brace at rear of engine bay)
-when I get back to it (I was able to park it in my brother-in-law's shop), I'm going to spray carb cleaner above each carb to check for idle change, check for spark on each wire (pull off distributor while idling), maybe a compression check, pull off distributor cap and look to see if anything looks off (I have an XR700 ignition). Those were some tips given to me by a club member. Anything else to try?

Have to ask: Do wheels all turn okay? When you let off gas does car slow abruptly, or does it coast? It could be a brake issue. I had a 64 sedan with a master cylinder issue. After driving a few miles (in town - stop and go) It would take more and more gas to keep going until it finally would barely move. I would pull over, crack a bleeder (or maybe it was the brake line?), and it was good for a few more miles. Dennis

If you have to turn the idle stop screws down 1 turn the carburetor is no longer using the idle circuit.
If the throttle plate is not in the idle position the vacuum advance port is not covered up.
I'm not sure how to address all the possible things that could be wrong. I'd want to verify that the timing is okay. With points and condensor I'd probably do that with the engine not running and using a 12 volt test light.
With the engine running it could be into mechanical advance at a relatively low RPM.

-checked and adjusted timing with a timing light (verified @16 degrees)

Was the timing off?

-timing seemed consistent at idle and it advanced when I revved the engine

Good

-I took the tops off the primaries and checked inside. Main jets weren't clogged, venturi clusters/emulsion tubes/idle jets were fine. Accelerator pumps work great.

Was the throttle linkage opening both carburetors? If the right link fell of the the left head was doing all the work, hence the higher left head temp.

-I've raised the idle speed about 1 whole turn

So even idle was wrong, and needed these changes?

-richened idle mixture about 1/2 turn (that seemed to at least steady the idle)

-swapped ignition coils (I already mounted it on the vertical brace at rear of engine bay)

Always good to keep GM used coils on the shelf for testing, since they hardly ever go bad. But the aftermarket coils do fail.

-when I get back to it (I was able to park it in my brother-in-law's shop), I'm going to spray carb cleaner above each carb to check for idle change,

Or propane, you are checking for vacuum leaks? Then it is BELOW the carburetor, not above. Also look at balance tube hoses, they fail often making lean mixture at idle

check for spark on each wire (pull off distributor while idling), maybe a compression check,

Always a good baseline check

pull off distributor cap and look to see if anything looks off (I have an XR700 ignition).

Look at cap for cracks/carbon tracking but these usually make a miss. Have a points plate w/parts to install to test if the XR700 is failing?

Those were some tips given to me by a club member. Anything else to try?

The rolling test to make sure the brakes are not dragging mentioned above.

Does the car perform correctly for the first X miles? Got an outboard motor tank or such to bypass the fuel system?

Swap carburetors left to right, although this is very hard in a 140, so save this for very last.

Thanks for the replies. It previously had a slowly dying idle but everything else was fine. I checked the timing with a timing light and it looked more like 20 degrees so I adjusted it to 16.

I've got Roger Parent linkage and it's been great; everything looks good with it. I was planning on spraying above the carbs to see if the idle changes but I like the idea of spraying around the balance tubes as well since I've never messed with them.

I raised the idle in the hopes of it helping with the eventual stalling, although I'm not the biggest fan of it since my idle speed is above 1,000 rpm! I also do have a points plate that I might put in just to see. These are all giving me good ideas to check on when I get back to it.

A spray bottle of water works good to find a vacuum leak. Using something flammable can help you find bad plug wires also.

So the water does ???

When the water finds the vacuum leak it will change the way the engine runs and sounds. It will not flood the engine unless the leak is so big that you don't need anything to find the leak.

I'd also look at fuel delivery or maybe even a vacuum leak. Spraying carb cleaner like you mentioned should help check for leaks, but I'd also double-check fuel pressure and make sure the carbs are getting enough fuel under load. If compression checks out, it might be worth inspecting the fuel pump or lines. Could be a lean issue that's not super obvious at idle but shows up under heavy load.

I hate not having closure so thought I'd update that I figured it out. The driver side carb must have had something in it that made it not function because I disassembled it and blew carb cleaner through the hole for the main jet and reinstalled to a good running engine again. I don't know what was in there because last week when I pulled the top off the carb (along with the main jet), everything looked fine. Anyway, thanks again for the tips!

Make sure the hose from the balance tube to the vent tube has not come off or broken (rotted). It too can lose vacuum if not intact affecting your idle.

I like to say a grain of sand in the wrong place can cause carburetor trouble.

Lane66Monza wrote: ↑Mon Sep 30, 2024 2:49 am Make sure the hose from the balance tube to the vent tube has not come off or broken (rotted). It too can lose vacuum if not intact affecting your idle.

Yes, definitely. That is one of the things I checked as well (they were fine). I might end up replacing those hoses anyway just due to age.

chris wrote: ↑Sun Sep 29, 2024 8:23 pm I hate not having closure so thought I'd update that I figured it out. The driver side carb must have had something in it that made it not function because I disassembled it and blew carb cleaner through the hole for the main jet and reinstalled to a good running engine again. I don't know what was in there because last week when I pulled the top off the carb (along with the main jet), everything looked fine. Anyway, thanks again for the tips!

Thanks for the update. Good to learn what it was. Sounds like the your car was running on three cylinders. Corvairs run amazingly smooth on just half an engine, but as you noted there is definitely a loss in power.

BTW -- Always a good idea to run an inline generic fuel filter (metal can, not plastic).