29 pontiac won't stay running

[Daniell68]

Hi all

I have a 29 pontiac that I have to keep the choke about 3/4 on to keep it running. I have checked the Ignition system and it all looks OK. I have been through the carb and all looks OK. It seems to be hitting on all six. I don't see any obvious vaccum leaks. Any ideas?

[Guest]

Most likely your primary jet is plugged. Remove the carb, take the cover off the float bowl, remove the three screws on the bottom to separate the two halfs. The short jet is the primary one. Remove it and blow the dirt out. Don't use a wire or anything other than air to clean it. Simple fix. Takes about fifteen minutes. Son't retighten the jet too much. It just screws into pot metal and you can strip the threads real easy.

[Daniell68]

Thank for the thought but I have aready done that. It helped a little but it still has to be choked to stay running. Do you have any other ideas.

[Guest]

If it still has to be choked your passage that feeds the jet could be partially plugged or your float could be set too low. This is of course providing your spring operated air valve is operating and set right.

[Mark Shaw]

I have exactly the same problem with my 29 Buick.

Marvel carburators are tempermental at best.

I have tried everything suggested here too, but you might also check to see if your vacuum line to the wipers is sucking air.

Let me know if & when you find your problem.

durcodude@comcast.net

[carbking]

One of the major problems often encountered (among many) with the Marvel carburetor is the swelling of the spacer block, preventing closure of the air valve. For proper idle, the air valve MUST be capable of complete closure.

To check this, the carburetor needs to be removed from the engine. With the carburetor removed, one should be able to manually open the airvalve, and when released, the air valve should SNAP closed.

If the air valve does not fit tight against the throttle body, the cause generally is the spacer block. This block is made of a poor quality zinc alloy, that swells with age. There is a finite clearance specified between the lower edge of the air valve, and the spacer block; but the swelling of the spacer block will eliminate this clearance and actually force the air valve open. This prevents idle air from passing through the idle venturi to pull sufficient mixture from the idle jet to give proper adjustment.

If this condition is present, it may generally be alleviated by placing a piece of 400 grit emory cloth on a piece of glass, and "sanding" the flat surface of the spacer block. The spacer block is retained in the body by two flat head screws, which must be removed to remove the spacer block.

Jon.

[Daniell68]

Hi all

Thanks for all your help!! After my 3rd trip into the carb I finaly found my problem. In the main jet there was a small spek of crud that I could not see. I could see light through the jet. It would not come out with cleaner or compressed air. I used a small length of copper bell wire and slid it throug the jet. Then I could see a lot more light through the jet. Now it runs better than it ever has. Thanks again.