The Ford Barn - View Single Post - Model a like a spirited colt or a carburetor problem?

P.S. · 05-06-2017, 10:58 AM

Does it still do that when the spark lever is all the way up (retarded)?

If it does: Possible vacuum leak. Check around the carburetor butterfly shaft and the intake manifold gasket. Also check vacuum wiper (if so equipped). Or, could be way too rich. Open up the air bleed. If the idle bleed adjustment won't get you there, it could be a blockage in that tiny passage that your butterfly is partially blocking.

If it does NOT: You are running too much advance. Assuming you timed your Model A the way Henry specified, your spark lever should only be a few clicks down at idle. The manual that came with your Model A says to run the spark lever about half way down for in-town driving and only all the way down when actually on the highway at highway speed. That, of course, assumes you are running a stock motor with stock head, valves, cam, etc. If you run a high compression head or a touring motor, you need to use even less spark advance or be prepared to go through head gaskets frequently.

Many Model A 'experts' run way too much advance. It is a common mistake.

05-06-2017, 10:58 AM	#8
P.S. Senior Member Join Date: Jul 2012 Location: Hazzard County Posts: 1,921	Re: Model a like a spirited colt or a carburetor problem? Does it still do that when the spark lever is all the way up (retarded)? If it does: Possible vacuum leak. Check around the carburetor butterfly shaft and the intake manifold gasket. Also check vacuum wiper (if so equipped). Or, could be way too rich. Open up the air bleed. If the idle bleed adjustment won't get you there, it could be a blockage in that tiny passage that your butterfly is partially blocking. If it does NOT: You are running too much advance. Assuming you timed your Model A the way Henry specified, your spark lever should only be a few clicks down at idle. The manual that came with your Model A says to run the spark lever about half way down for in-town driving and only all the way down when actually on the highway at highway speed. That, of course, assumes you are running a stock motor with stock head, valves, cam, etc. If you run a high compression head or a touring motor, you need to use even less spark advance or be prepared to go through head gaskets frequently. Many Model A 'experts' run way too much advance. It is a common mistake.