hi guys, i have a problem with a holley. 80508. 750cfm. always running rich at idle since cam change. i discovered this carb comes with a 6.5 power valve, and my engine in gear at idle pulls about 5# vacuum. i found and installed a 3.5 power valve. now it wont run, like its dumping fuel into the engine. it did fire, got a lot of "raw" fuel out exhaust and ran very poor missing and sputtering. i swapped it back to the 6.5 but it still wont run. it seemed like a simple swap but could there be something i missed or wronged? i drove the car to the parts store to pick up the 3.5 power valve, about a 22 mile round trip without any problem. it all started when i pulled the fuel bowl.

any ideas?

Floats stuck?????

Steve O.

no they dont appear to be. they move when i take the bowl off. no fuel puking out the overflow. fuel at the bottom of the level plug. spark plugs are wet with fuel.

Same thing happened to me. Doing the same service. Try changing the 2 gaskets on the front of the carb, then take the power valve out and re-seat it's gasket, being very certain that it is centered correctly. I had a very small rip in 1 gasket and the PV gasket was off center. My car was literally pumping gasoline out of the #8 cylinder.

Also if it is the same problem I had, all 8 plugs will be fouled. Pull em all and clean em up.

Yes, all 8 plugs are fouled. will have to get new gaskets, will do this weekend. thanks for the tip.

According to Holley 5" of vacuum should have a 2.5 power valve.

found the problem....looks like the power valve gasket wasn't thick enough, and the body of the valve was making contact with meter block. appearing tight but not sealed. 3.5 valve in now and runs good, but wont idle on the idle circuits alone. need to crack the throttle plate screw open about a quarter turn to idle around 650 rpm. with plates all way closed idle is rough 400-450 and dies when in placed in gear.

found the problem....looks like the power valve gasket wasn't thick enough, and the body of the valve was making contact with meter block. appearing tight but not sealed. 3.5 valve in now and runs good, but wont idle on the idle circuits alone. need to crack the throttle plate screw open about a quarter turn to idle around 650 rpm. with plates all way closed idle is rough 400-450 and dies when in placed in gear.
This is a little old so you may have figured this out already if you have any holley mod books.With the idle raised for bigger cams you could be idling on the secondary idle circut or(idle transition circut)and get a stumble when comming off idle.A fix would be to drill a hole in each primary butterfly.About 3/16.This will eliminate the need to raise the idle with the screw and give a smooth trasition from idle when accelorating.It works.Your 650 rpm seems a little low even for a stock cam.