Power valve in a holley Double pumper 750

seventy468

Someone please explain what a power valve is/does. Keep in mind I am still learning, so be nice! I also see holley offers a power valve block off to get rid of the power valve, for racers? This car is a street strip car.

af2 · Posted: Thu Aug 20, 2009 9:08 pm Post subject:

Keep it and tune it to the vacuum you run off idle to half throttle. With a cam usually a 5" will do it.

seventy468 · Posted: Thu Aug 20, 2009 9:22 pm Post subject:

if you have a back fire threw the carb, does that usually ruin a power valve? and a bad power valve will have what symptoms?

10sec.et · Posted: Thu Aug 20, 2009 9:51 pm Post subject:

it certainly can ruin the PV. there are kits to prevent damage to the PV with a little check ball and spring. i used to think those little PV saver kits were the greatest thing since sliced bread, until today. i took my 850 DP apart for some "tweaking" and noticed that both check balls were gone from the factory installed kits Shocked

. the spring and washer were there but i guess my engine has ingested the little check balls Evil or Very Mad

. at this point, im thinking ill just keep a couple extra power valves in my tool box. no, im not tearing into the 455 looking for them.

MufflerBearings69 · Posted: Fri Aug 21, 2009 8:27 am Post subject:

lun40119 · Posted: Fri Aug 21, 2009 7:01 pm Post subject:

OP, the power valve supplements the main circuit during tip, and during WOT, or any other time the manifold vacuum drops below the stated value of the pv. They are a great thing, they allow you to tune your part throttle AFR, with the primary jets, and not affect the wot tune. I like to cruise lean, but use the power valve channel restrictors to enrich the main circuit during wot. If you are going to try to tune with the pvcr, it is a good idea to have a wideband, either a handheld or on a chassis dyno. I like to use a chassis dyno. I hope this makes sense, it does in my head.

clay · Posted: Sat Aug 22, 2009 10:34 pm Post subject:

Pretty much summed up operation but here's a quick way to check it before you put it on the engine. Put the carb on a stand and fill the bowls through the vent tubes. If the valve is ruptured or the gasket is leaking there will be fuel running out of the bottom coming from the vacuum port that leads to the power valve chamber. I have had two power valves really kick my butt. One had threads that weren't cut quite far enough and when the valve snugged down, it hadn't pinched the gasket. Finally found it with a feeler gauge between the gasket and valve. Another one had a nylon gasket and there were 4 indentions where I'm assuming pins had pushed it out of the mold - leaked just enough that the idle mixture screws wouldn't do anything. Clay

lun40119 · Posted: Sun Aug 23, 2009 8:23 pm Post subject:

Another way to check it on the engine is to make sure it is all the way down into the idle circuit. The turn the idle mixture screws all the way in, if it doesn't quit, that means that the PV is supplementing. If it quits, you are fine.

On a lighter not, I have stopped using the checkballs in the base plate. On my last engine I had a cam in it that was pretty dirty down low. Lots of overlap, anyway long story short reversion at low gramma putt, putt rpms caused the checkball to stick in the baseplate creating a NASTY lean WOT tune. Popcorn anyone!!!!!!

10sec.et · Posted: Mon Aug 24, 2009 12:23 am Post subject:

nomad239 · Newbie Joined: 01 Jul 2007 Posts: 7 291.86 points

TO PICK THE RIGHT PRIMARY PV TAKE A VACUUM READING AT IDLE.GET A PV THAT OPENS 2" LESS THAN THAT VACUUM READING IF YOU ARE RUNNING TWO PV'S THE SECONDERY PV SOULD BE ANOTHER 2" LESS.THIS WILL MAKE GOOD POWER AND DRIVEABILITY AS WELL AS FUEL MILEAGE.

robins44 · Member Joined: 29 Dec 2007 Posts: 603 17699.76 points

squeeezer · Posted: Mon Dec 06, 2010 12:45 pm Post subject:

^^^^^^^^^that can be used for a generic starting point

not absolute

some people go with 1 inch lower that idle

some (and i dont get this one) go with 1/2 idle vacuum

if i do it for mileage(you got the wrong carb for that)you drive around with a vacuum gauge taped to your windshield and taylor it to your driving style

MufflerBearings69 · Posted: Mon Dec 06, 2010 4:35 pm Post subject:

squeeezer · Posted: Mon Dec 06, 2010 5:50 pm Post subject:

yeah what he said^^^^^^^^^^^^^^^^

MufflerBearings69 · Posted: Mon Dec 06, 2010 8:21 pm Post subject:

I came back to make sure I didnt come across wrong- I wasnt upset or trying to argue- just saying, some of the books on the market have some weird crap in them... Just because its published doesnt make it golden right?