i am having trouble with my holley 600. it was rebuild about 5000 miles ago, but sat for about a year in between engines.

It is running way too rich. I am going to try to adjust the float levels again, but could a blown power valve dump too much fuel?

As soon as i evern step onthe games, the car surges and today i even got a backfire at 30mpg. Even when i hold the throttle steady, i can feel/hear a slight miss or something in the exhuast. What could cause this? even the idle mixture screws dont seem to do awhole lot at all.

Is it possible the carb cant supply enough fuel or i am getting a weak vacuum signal due to cam and heads?

do have a simple rebuild kit with some old trick kits that i can replace the gaskets, and power valve, etc.

Could be the power valve,yes. Mine did that when it blew/had a small hole in it.

more than likely you've blown the power valve in your carb . if it's stumbling really bad and running very rich that's another indication of a bad power valve .another thing is holley carbs don't like sitting dry for a long period as the seals/gaskets tend to dry out and get damaged by the fuel

first thing i would do is pull the bowls and re-gasket them and while your at it replace the needle/seats and power valve .doing that should clear up the problems you're having

more than likely you've blown the power valve in your carb . if it's stumbling really bad and running very rich that's another indication of a bad power valve .another thing is holley carbs don't like sitting dry for a long period as the seals/gaskets tend to dry out and get damaged by the fuel

first thing i would do is pull the bowls and re-gasket them and while your at it replace the needle/seats and power valve .doing that should clear up the problems you're having
couldnt of said it better.

will do that tomorrow. how do u selected the correct power valve again? isn't take your vaccum and divide by 2?????

Also what squirter and jet size would u recommend as a starting point?

thanks
mike

I'm purdy sure its take the vacuum and subtract 2.

so i am at 10 vaccum so i would want a 8 power valve? it has the 6.5 in it if i recall.

oops

81, you were right. its take the vacuum and divide by two. Read this, its right off holley's FAQ section.

QUESTION How do I tell what size power valve I need?
ANSWER To properly size a power valve, take a vaccum reading at idle and if it is above 12" for a standard transmission a 6.5" will be safe to use. For automatic transmissions take a vaccume reading in gear at idle and if the vaccum is below 12" divide that in half for proper size. Example 9" of vaccume in gear at idle will require a 4.5" power valve.

so i will try to get a 5.5 then. hope i have one.

i would also recommend a red pump cam in the #1 position and use a #31 squirter

My car has 10" @ 1,000 and had a bad hesitation with the factory 4.5 that came in my carb I switched to an 8.5 and the world has never been better to me.

i think i have a 31 squirter and around 68 jet. I also think it has the orange cam. We had it up to 34 squirter and about a 75 jet when we first rebuilt it, but i backed it off, for fuel mileage. I will have to take it off tonight and see what i can do.

hollys are known for blowing power valves, im in the process of rebuilding mine now. My rear floats were kinda fucked..

pulled the float bowl off today, and replaced power valve, increased jets to 69 and replaced idle mixture screw corks. Also adjusted float levels.
The power valve was shot.
It runs great now. Just need a few more miles before i let her eat.

How many miles do u think i need on it, before i can see what it can do? It is a solid roller cam, with new rings on honed block? i was going for 500 miles.