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Old 01-04-2012, 08:38 AM
chrisjkruse chrisjkruse is offline
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Default Re: Rochester Carb Adjustment

Yes, you are not getting enough fuel at idle. All fuel enters the engine by the manifold vaccuum and the velocity of the air creating a low pressure (venturi effect) which draws the fuel thru the jets. (except when the throttle is opened quickly, then there is a piston that squirts fuel down the throat of the carb to compensate for the momentary vaccuum drop that takes place)
There are idle jets at the bottom of the carb which are smaller and are the first jets to operate . More air speed/volume is required to draw fuel from the larger/higher jets above these.
By choking off the air flow you are forcing more fuel into the carb-(Not from the venturi effect-but rather like sucking on a straw.) Fuel will enter thru all of the jets.
My guesses are:

A. The idle jets are clogged
B. There is not enough vaccuum to operate the carb effectively.
1.( you mentioned something about vaccuum advance.) Make sure that your ignition timing is correct.(there probably is a vaccuum advance)
2. Make sure that there are no more vaccuum leaks.
3. Check that the timing chain has not jumped a few teeth.
4. Satisfy yourself that the carb gaskets are in good shape( both within the carb and where it mounts to the manifold. Also the intake manifold gaskets.
5.Do a compression test to determine if there are valve, head ,or head gasket problems. ( If it can't compress..than it cant suck either!) i should get a t-shirt with this on it.
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