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 PV would make it run rich, but it would not allow you to screw the mixture screws all the way in and still have the engine run. There is something else wrong causing that. There isn't anything you can see that will indicate a PV being blown or not, you'll need to remove it and actually check it.
The way the idle circuits are designed if everything is working properly all of the fuel the engine gets at idle should come from your curb idle discharge ports. These are controlled by your idle mixture screws. If they are shut the engine should not be getting enough fuel to idle. If it does you have a problem. It can be that the butterflies (front or rear) are exposing too much of the transfer slots pulling fuel into the engine. It could be the float level being set too high, and pulling raw fuel out of your boosters at idle. It could be a bad PV gasket causing raw fuel to leak into the engine. A blown PV would leave it in the "open" or flowing position adding fuel to the main fuel well which is where the idle circuit gets its fuel from. This would cause a rich idle, but would not allow you to completely shut your idle mixture screws.