Carb issue one carb lean or vacuum leak

[kris]

Hi, so I spent the winter getting my 1962 pg to run, last driven 2008.
I've got it running and driving but am having trouble with one carb.

When running I place my hand over the top of the carb completely choking it off it will pick up a some rpm and run better. When I do this to the other carb it wants to die and acts the way it should (how I think it should anyhow).

So the suspect carb must be lean.

- I swapped carbs from right to left and the problem followed the carb.

- I disconnected balance tube and pinched off rubber tube isolating it to carb.

- I made sure the carb base spacers were flat and put on new gaskets of bolts sides of spacers.

- I then put a rubber o ring around one side of the throttle shaft no change.

- I have rebuilt these carbs

- I pulled the carb apart today and blew out all passages with compressed air and have also triple set float levels

- I have taken a bottle of propane over ever nook and crannie of the carb and cannot find the leak

- I have sealed off/ isolated the choke and advance ports

-I have retightened carb top screws


When I put my hand over the carb I can hear the air coming from somewhere ??? Hand over carb and can't find it with propane.... I'm at a loss,
By I know one of you gurus can help!

Kris

Revelstoke BC

[Jerry Whitt]

Go back to basics.
Do a compression test on all cylinders.
The pressure readings should be pretty close all around. If not, you may have located the problem.
Check dwell. Should be around 30 degrees. Check timing with vacuum advance hose disconnected. While engine is running, is there vacuum to the vacuum advance unit? Should not have vacuum at idle, only when throttle plates begin to open.
Now test carburetor air flow with a meter. If the numbers are way off, adjust the idle speed screw of the low reading carburetor to get matching flow.

Let us know your test results.

[bbodie52]

Have you checked for a faulty plastic choke pull off (vacuum break) diaphragm? An internal leak or a crack or faulty plastic housing could be permitting a vacuum leak through the hose to the vacuum tube at the base of the carburetor. Also check the condition of the rubber hose to ensure that it is not split and permitting vacuum leak. Other vacuum diaphragm units on your Corvair that can leak and cause problems include the vacuum advance on the distributor and the vacuum modulator on the right side of the Powerglide transmission.



http://www.corvair1.com/1962-69-choke-p ... each-rfs20

http://www.corvair.com/user-cgi/catalog ... ow_page=55



Also check out the following...

Tricky Vacuum Leak
viewtopic.php?f=55&t=2644

Mon Sep 12, 2011 7:05 pm



The problem was a clogged tube in the venturi cluster. I ran a thin wire through and blew it out with compressed air. Idles great now!

[bbodie52]

- I have sealed off/ isolated the choke and advance ports...

I missed your comment about isolating the choke and advance ports. The clogged venturi cluster tube suggestion might still be applicable.

[kris]

Go back to basics.
Do a compression test on all cylinders.
The pressure readings should be pretty close all around. If not, you may have located the problem.
Check dwell. Should be around 30 degrees. Check timing with vacuum advance hose disconnected. While engine is running, is there vacuum to the vacuum advance unit? Should not have vacuum at idle, only when throttle plates begin to open.
Now test carburetor air flow with a meter. If the numbers are way off, adjust the idle speed screw of the low reading carburetor to get matching flow.

Let us know your test results.

Compression every cylinder dead on 150 psi except one at 140.

Dwell I repeatedly set until dead on the number in the shop manual 34 degrees I believe

Brand new distributor including vac cannister I'll double check but I have observed it operating properly multiple times



Now idle speed it could be... I have read multiple times on here how to balance carbs.... And I still don't know if I fully understand what is supposed to be achieved for idle speed, as it's usually set with paper just dragging then turn in x amount of turns...
What I really want to know is out of the spark port ( top port ) is there a vacuum reading I should have? I thought it was zero because throttle plates should be closed...

Actually now I remember when I was tuning it the trouble carb would not idle low enough with the idle speed screws opening the throttle plate at all it would rev to high.... Further making me think there is a vacuum leak... Or to lean.

Both carbs are set up the same way so that I could get my low idle /no clunk into drive.


Also just to confirm to the other poster, the carb has all ports blocked off I had balance tubes blocked off but now not as it doesn't make a difference.


I previously blew air through venturi cluster but it could be partially blocked, might have to find some super thin wire that's strong enough... But at idle the Venturi isn't activated is it? And this is when I'm having the condition, I can see a fairly equal amount of gas from each carb (from ventures) with throttles cracked.

Also the suspect carb doesn't react to idle mixture adjustments very well, I can turn the idle mixture screw in and it doesn't stumble and die like the other carb.

Thanks for your help so far!

[kris]

Go back to basics.
Do a compression test on all cylinders.
The pressure readings should be pretty close all around. If not, you may have located the problem.
Check dwell. Should be around 30 degrees. Check timing with vacuum advance hose disconnected. While engine is running, is there vacuum to the vacuum advance unit? Should not have vacuum at idle, only when throttle plates begin to open.
Now test carburetor air flow with a meter. If the numbers are way off, adjust the idle speed screw of the low reading carburetor to get matching flow.

Let us know your test results.

Compression every cylinder dead on 150 psi except one at 140.

Dwell I repeatedly set until dead on the number in the shop manual 34 degrees I believe

Brand new distributor including vac cannister I'll double check but I have observed it operating properly multiple times



Now idle speed it could be... I have read multiple times on here how to balance carbs.... And I still don't know if I fully understand what is supposed to be achieved for idle speed, as it's usually set with paper just dragging then turn in x amount of turns...
What I really want to know is out of the spark port ( top port ) is there a vacuum reading I should have? I thought it was zero because throttle plates should be closed...

Actually now I remember when I was tuning it the trouble carb would not idle low enough with the idle speed screws opening the throttle plate at all it would rev to high.... Further making me think there is a vacuum leak... Or to lean.

Both carbs are set up the same way so that I could get my low idle /no clunk into drive.


Also just to confirm to the other poster, the carb has all ports blocked off I had balance tubes blocked off but now not as it doesn't make a difference.


I previously blew air through venturi cluster but it could be partially blocked, might have to find some super thin wire that's strong enough... But at idle the Venturi isn't activated is it? And this is when I'm having the condition, I can see a fairly equal amount of gas from each carb (from ventures) with throttles cracked.

Also the suspect carb doesn't react to idle mixture adjustments very well, I can turn the idle mixture screw in and it doesn't stumble and die like the other carb.

Thanks for your help so far!

[toytron]

When you check the carb for clear passages I find it best to use a carb cleaner instead of just air. When using air only you may not get a good picture of how the pattern looks of the flow from the passage. I would suspect that your problem may lie in the idle circuit.



This came from the Delco Rochester manual 0151-433B




Ed Stevenson

[terribleted]

I have seen similar symptoms many times. Hand over 1 carb engine barely changes rpm...may speed up a little may slow just a little but no real noticeable difference. Block other carb and it dies right away. The problem is in the carb that does not react. There is a blockage in the base.

The key here is that you swapped the carbs and the problem stayed with the carb. You have a blockage in that carb. It may be effecting idle only or overall function. Are you sure that side of the engine is operating? What I mean is does it get hot evenly with the other side, or does it warm much more slowly and stay cooler? How is the power when driving? I have had new Corvair owners operate on 3 cylinders and not even realize it until they operate the cars on 6 since the cars operate so smoothly on 1/2 the engine:) Sometimes a blockage can be dislodged by revving the engine and slapping a palm over the offending carb.The quick changes in pressures and suction will sometimes unblock things. Disassembly, re-cleaning and re-checking adjustments sounds like it is in order unless something like the slap trick works.