Flathead doesn’t idle right

Re: Flathead doesn’t idle right

Does your distributor have a vacuum advance cam? An engine with a more aggressive cam generally needs more initial advance. I would say in the 6 - 8 degree range. But this may give you more advance than needed at higher rpms.
 
Re: Flathead doesn’t idle right

flatjack9 said:
Does your distributor have a vacuum advance cam? An engine with a more aggressive cam generally needs more initial advance. I would say in the 6 - 8 degree range. But this may give you more advance than needed at higher rpms.
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No It doesn’t, this might be stupid question which way on the distributor is advance?
 
Re: Flathead doesn’t idle right

We need more information; Early (front-mounted) or Late (conventional "post"type"). If the former, it should be set up and timed on a machine intended for that purpose. If the latter, CCW to advance, CW to retard.
 
Re: Flathead doesn’t idle right

tubman said:
We need more information; Early (front-mounted) or Late (conventional "post"type"). If the former, it should be set up and timed on a machine intended for that purpose. If the latter, CCW to advance, CW to retard.
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It’s a later motor with the distributor on the side of the motor,
 
Re: Flathead doesn’t idle right

KiWinUS said:
What distributor are you using? Stock is a bad choice
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Especially if you are not running a bone stock carburetion system.

And who does that with a "hot cam"?:confused:

If the distributor is from "Bubba" it's most likely a modified SBC unit. Is it mechanical advance only or vacuum over mechanical?
 
Re: Flathead doesn’t idle right

tubman said:
Especially if you are not running a bone stock carburetion system.

And who does that with a "hot cam"?:confused:

If the distributor is from "Bubba" it's most likely a modified SBC unit. Is it mechanical advance only or vacuum over mechanical?
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I wish I could understand what does this mean, I am confused on this distributor,
 
Re: Flathead doesn’t idle right

Most modern distributor have two methods of advancing the spark timing. There is a set of internal weights that move outward when the speed increases that causes the timing to be advanced as engine speed increase (this is called the "mechanical advance"). In addition, they usually have a vacuum advance unit that also advances the ignition timing as manifold vacuum increases. Vacuum is highest at engine idle and steady cruise, and the additional advance it adds to the mechanical advance provided by the weights serves mainly to increase fuel economy. In periods of low vacuum (acceleration), the advance is limited to that provided by the mechanical advance only to prevent detonation under load.

Just about all SBC distributors come with vacuum advance. You can tell because they have a vacuum line running from the intake manifold to the advance unit on the side of the distributor. The attached picture is not very good, but you can see part of the vacuum advance. It is the round silvery-gray unit at the back of the distributor. I mention this only because I believe "BUbba" is kind of a fan of mechanical only setups so it may have been removed from your distributor.
 

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Re: Flathead doesn’t idle right

tubman said:
Most modern distributor have two methods of advancing the spark timing. There is a set of internal weights that move outward when the speed increases that causes the timing to be advanced as engine speed increase (this is called the "mechanical advance"). In addition, they usually have a vacuum advance unit that also advances the ignition timing as manifold vacuum increases. Vacuum is highest at engine idle and steady cruise, and the additional advance it adds to the mechanical advance provided by the weights serves mainly to increase fuel economy. In periods of low vacuum (acceleration), the advance is limited to that provided by the mechanical advance only to prevent detonation under load.

Just about all SBC distributors come with vacuum advance. You can tell because they have a vacuum line running from the intake manifold to the advance unit on the side of the distributor. The attached picture is not very good, but you can see part of the vacuum advance. It is the round silvery-gray unit at the back of the distributor. I mention this only because I believe "BUbba" is kind of a fan of mechanical only setups so it may have been removed from your distributor.
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It does not have a vacuum like the picture,
 
Re: Flathead doesn’t idle right

You have a very good distributor. I doubt it is creating your sooty plug issues. You will always have misfire with sooty plugs.
 
Re: Flathead doesn’t idle right

If you have excessive fuel running into engine from just one or both carburetors could cause your misfire at idle.
Because you have plug fouling issues I personally believe it’s a carburetor problem.
 
Re: Flathead doesn’t idle right

KiWinUS said:
If you have excessive fuel running into engine from just one or both carburetors could cause your misfire at idle.
Because you have plug fouling issues I personally believe it’s a carburetor problem.
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If this is the case, I think this might be a good time to install a stock manifold and run each carburetor separately to get a better handle on it.

Also, since the distributor seems to be mechanical only, I'd go with my first suggestion for timing.
 
Re: Flathead doesn’t idle right

tubman said:
If this is the case, I think this might be a good time to install a stock manifold and run each carburetor separately to get a better handle on it.

Also, since the distributor seems to be mechanical only, I'd go with my first suggestion for timing.
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Ok, I think I know what might be my problem, one of my carb doesn’t shoot as fuel out of two port, as my other one, I am thinking it could be my power valve,
 
Re: Flathead doesn’t idle right

Power valves must function correctly & be sure you used the correct gasket for power valve.. could very possibly be your issue.
cheers Mate
 
Re: Flathead doesn’t idle right

After all of this, we are missing one important piece of information. Has this engine ever run well? It sure sounds like a fresh rebuild that you can't get to run right. Unlike the pros ("RonnieRoadster" in particular), most of us have a problem getting a new engine up and running with multiple carbs.

Do yourself a favor and beg, borrow. or steal a known good stock intake system.
 
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