Originally Posted by leejoy
Dear Mr. Tech
I already did the first part of your message, now I can test the accelerator pump idea and see what that does. good idea. I may have a blown power valve. I need to help to explain. If it is blown I can see why i'm having these problems. I think when the idle mixture screws are turned all the way in there is little or no change to idle if I recall......indicating a blown (open-ruptured) power valve right? what I don't understand is if the power valve is not blown, but open, how would that affect idle? At idle it's just drawing through the idle ports anyway and so what if the power valve is open. I don't understand.
A blown power valve (sometimes happens when the engine backfires) will allow extre raw fuel to dump into the engine. The power valve is there to help the transition from idle and low throttle positions to moderately opening the throttle when you don't hammer the throttle enough to get a big squirt from the acellerator pump. When I am having problems like you are having, Holley has screw in plugs that I install in place of the power valves and go up 2 to 4 sizes on the jets.
If you are getting a really rich mixture as you would get with blown power valve, it is likely you have opened the primary throttle with the idle screw just to get it to start. It would be a very rich and smelly idle. You could achieve the above described idle condition with the idle air screws all the way in and the throttle plate idle screw cracked open.
There is a good book, Super Tuning and Modifying Holley Carburetors by Dave Emanuel which will teach you all you need to know. Then you won't have to share the women with dirty old men like me.