ok i took my car to the paint shop and i pick it up saturday......my carb is messed up and my motor wont run so i towed it there....ok now from what i hear i prolly blew my power valve becauuse my carb backfired like 20 times when trying to get the timing right on the cam swap.....i have a 1850 4160 holley......where is the power valve on it.....could i change it in the parking lot....which one should i get...i got a 305 w/600 holley 4160, 1 inch spacer, 266 energizer cam, edelbrock intake, headers, exhaust when sring rolls around....just gotta weld up the hooker system.....so how hard is it to swap, where is it, wand what size should i get?

 

In the primary metering block, behind the primary fuel bowl.

I can change one just about anywhere, if I have the tools.... something the get the fuel line off, and a kind of large screwdriver, and a 10" or so Crescent wrench or 1" open-end.

Get a 8.5 one.

 

Go here for a picture http://www.holley.com/HiOctn/TechSer.../f4150-60.html

1) Remove fuel line.

2) Remove 4 bowl retaining screws (when you remove the lower ones, fuel will come out).

3) Pull back the bowl, separate the bowl and metering body. Watch how things are oriented, go to the picture if needed. The balance tube going back to the secondary bowl should stay with the carb (hold it in place as you pull the bowl away - it doesn't really matter if it comes out of the secondary, though).

The power valve is on the carb body side of the metering body.

Your carb probably came with a 6.5 PV.

 

what do power valves do....regulate fuel??..how would a 8.5 work better than a 6.5 or even a 5.5....

 

They stay closed whenever the vacuum is above that number, and open when it is below it. That richens the mixture when you open the throttles more.

The ones they put in stock Holleys are always too low.... they are based on the days when people would put a "¾ race" cam in their otherwise stock 283 or (gasp) 327, and then couldn't make it stop blowing out black smoke at idle, because the vacuum was so low the PV wouldn't stay closed. Problem is, with the PV staying closed until you open the throttle far enough to make the vacuum drop that far, you've already endured a biiiigggg looonnnnnggg flat spot or bog; most people will try to richen the jets to cure that, then wonder why their gas mileage is measured in gallons per mile instead of miles per gallon. Most Holleys come with a 6.5 which is just simply too low. Nearly every car I've tuned with a Holley on it (not that many, probably no more than 40 or 50 I'd guess) ran about 100 times better and got acceptable gas mileage by leaning the jets and raising the PV number.

 

good job explaining that...thanks.....i think ill go with the 8.5 then.....you sound like you know what your doing...lol.....i know all the basics but im still a youngin so i dont have any experience

 

After reading this thread a few days ago, I got a 8.5 PV from a friend of mine and stuck it in my carb. Very noticeable improvement in drivability