AntiRiceRacing

Well my power valve on my holley is ****, should i replace it or block it off? If not, what size powervalve should i get for a holley 700cfm?

mjr46

heck they are only a few bucks for a new one....as for what size, you normally use a vaccum gauge and see what the reading is and half that = power valve size

AntiRiceRacing

I dont have a vacuum gauge.. what if i was to buy one that is to big or to small? The carb is a holley 700 double pumper..

JD1969

The car will run rich or lean or might have other issues if the power valve is not sized right. If the car was running good, just replace it with the same size. On a side note, if you go with a block off, you will need to jet up approx 4 sizes. BTW, it an easy job to install a PV blow out protection, Summit sells them.

wagontrain

Do not block the power valve off,it will not have the proper A/F ratio thru out the entire range.With out getting to in depth,emulsion tubes and air bleeds are not set up for adding that much jet and in most cases it could be up to ten jet sizes larger. Generally, Holley installs a 6.5" power valve ,which works in most cases.If the base plate does not have a backfire check valve in it,it is very easy to add one.Then figure out why it is backfiring,so as to not ruin anymore.

mjr46

so go buy a gauge. Judas!!!they are cheap too., proper diagnosis and repair begins with the use of proper tools for verification

tinman

Most Holley power valves have it stamped on them what 'size' they are. It's down by the flats on the thing. Look for something like '65' or '70'. Meanig 6.5 or 7.0.
I wouldn't do the power valve plug thing for a couple of reasons.
1) If they were a good idea, Holley would have built them that way.
2) I've tried it and there is always a bunch jetting problems, just making for a lot of make work..

67mustang302

What they all said.

And you really, REALLY don't want to block off your power valve.