Hey guy's....
How can you tell if the power valve on a Holley is bad.....?

Black smoke from exhaust.
VERY rich, poor idle.
Fuel fouled spark plugs.
Fuel in oil.

When all else fails, Moroso makes a nice tester for use with a vacuum pump.


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Don~ ZZ430DropTop (http://hometown.aol.com/zz430droptop67rs)
~~~~and~~~~
Pro-Touring.com DropTop (http://pro-touring.com/featured_cars/Camaro/1967_Camaro/Don%20Seefeldt%2067%20Camaro/don_seefeldt.htm)
67 RS/SS Convertible, 70 RS/Z28

[This message has been edited by ZZ430DropTop67RS (edited 12-13-2001).]

On the car: Poor driveability...usually when the power valve is bad it is from the rubber diaphram becoming hard....either from age....or more common , any backfire through the intake.....once the diaphram is hard it can either not allow the valve to seat , which allows fuel to go through when the valve is supposed to be closed...unwanted rich condition...black smoke out exhaust at idle or just cruising down the street....or....not allow the valve to open all the way...unwanted lean condition....at full throttle...loss of power , lean "pop" through exhaust..

Off the car: I have a checker that is used with a hand held vacuum pump....I got it through either summit or jegs years ago....works pretty good....

If questionable....just replace it.....any holley guy should have spares as well as spare gaskets......

Maybe somebody else can add to this....whew....it's hard to condense tech conversation into few words......Billy

SSuperman,
you can make a simple vacum chamber out of a piece of 3 or 4 inch pvc pipe and a couple end caps glued to the ends of the pipe. Drill and tap one end and install the correct fitting to attach to your vacum pump and drill and tap the other end for you power valve. I use the vacum chamber for all kinds of tests, it works great.

Did you modify your engine with a long duration camshaft or large plenum intake manifold? If the problem you are having is at idle, check you engine vacum at the manifold and make sure the power valve you are using is at least 2" lower rated than the idle vacum. Otherwise it could be opening at idle and causing you to run too rich a mixture. My 332 with crossram and .540 lift 312 duration solid cam engine had this problem, only pulling around 7 inches at idle and the valve was rated at 6.5 inches, it ran really rich.
Dave

This one is much easier. Push in the power valve, put that end in your mouth, and suck on it, so it sticks to your tongue. Slowly release the pressure in your mouth. If the power valve sticks to your tongue, it's a keeper. If it falls off, try a few more times, just to make sure you had good suction. If you can't get it to stay on your tongue, throw it in the trash can, and buy a new one.

Spames is right, these things are cheap and easy to get to. If I even suspected it, I'd replace it. His test is what we call in aviation an operational test to see if it works, the other tests proposed are functional tests to see at what value the valve opens and closes. Because it is so cheap you can replace the valve quicker and cheaper than building the test equipment I proposed. I just do the ops test.
Dave

make sure when you replace it you install the valve with the picture window holes in it, they are large square holes. Dont use the one with several small holes in it even if that's what was in your carb. I don't know if they're even still available. Also make sure you use the correct gasket for the picture window power valve.

It's a good idea to check them before installing, as I've seen new ones not in spec, and even completely inop!
Use a vacuum pump with gauge to see if they really open when they're supposed to.

------------------
Don~ ZZ430DropTop (http://hometown.aol.com/zz430droptop67rs)
~~~~and~~~~
Pro-Touring.com DropTop (http://pro-touring.com/featured_cars/Camaro/1967_Camaro/Don%20Seefeldt%2067%20Camaro/don_seefeldt.htm)
67 RS/SS Convertible, 70 RS/Z28