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Author Topic:   Alky Carb
posted February 10, 2004 11:07 AM
Contact KPLUGNUT. I hear he can fix that problem.

posted February 10, 2004 11:44 AM
What is your fuel pressure at idle?
At idle ours jsut bounces off 0.

The steel needle and seats used in alky carbs dont seal as well as the viton needles. At idle and with excess fuel pressure fuel levels will creep up and do exactly what you are talkign about.

There are other possibilities as well but i would check into this first.

posted February 10, 2004 11:50 AM
if the fuel is coming from the accelerator pump shooters, it is possible that the vaccuum through the carburetor is draw the fuel out. i have seen this happen before (though only ever on 4 cylinder engines). if it is the case you can fit "anti pull over" pump shooters or as a quick fix, file or sand the shooter legs back so that they are no longer sticking out.

posted February 10, 2004 01:27 PM
You do not need 6-9psi at idle for alky. 3-4lbs at idle is fine, but you'll only get that kind of pressure when running a belt drive pump. Mechanical pumps usually idle at more than 7lbs to begin with and gain to as much as 15lbs at WOT.
What you've got is a classis case of "pullover".
You'll first want to set up your idle circuit properly, as your butterflies are open too far (exposing too much of the idle transfer slot at idle) and that is what is causing booster "dribble".
Firstly, what carb is it, and is there any holes drilled in your primary butterflies? If so, what size are they?
Next, you should remove the carb and view it from underneath and let us know how much of the idle transfer slot is exposed by the butterflies when they are closed. This is the vertical slot in the baseplate bore that gets partially or mostly covered up when the butterflies are closed.
Give us some more info and I'm sure we can cure you.


posted February 10, 2004 03:03 PM
Just wanted to clarify some things,

Are the 5/64" holes in both primary and secondary sides?

Also how much of the transfer slot is showing on the primary and secondary? Can you judge whether the length it is showing is more or less than the width of the slot?

Where are the idle screws set at, turns out from closed?

Is the fuel dripping from the primary or secondary booster? or both?

posted February 11, 2004 09:35 AM
Dirtbuster beat me to it. Those are the questions we need to get answered in order to find the source of the problem.
A 5/64" size hole should be close but you'll have to verify how much of the transfer slot is showing (when viewed from underneath the carb). Just like Dirtbuster said.
About .025" is what the width of the slot is, so you'll want about that much vertically showing when the butterflies are closed.
Next (after verifying your idle fuel pressure isn't too high), you'll need to set the idle mixture screws properly, either via the vacuum method (reading where max manifold vacuum is achieved when adjusting each screw) or just start with each screw 1 1/2 turns out from lightly seated and adjust slightly from there until you get what seems like the best rpm at idle.
A float level that is too high or fuel pressure that is too hight at idle is usually the most common cause of alky fuel pullover, with the next most common cause being a need to close the butterflies down further on the slots.
Be CAREFULL not to drill the butterfly holes too large, as the engine will idle too high even with the curb idle screw backed all the way out.

Hope that helps, and let us know.


posted February 11, 2004 10:52 AM
KPLugnut Dirtbuster.. 5/64 holes in the primaries and secondaries. I will have to pull the carb off tonight and check the transfer slots. Boosters dibble mostly from primary sometimes secondary. I will also check the idle mixture screws. The floats seem to be ok, fuel just barely runs out with the screw removed. Fuel pressure 2-4 psi at idle.