Test Holley power valve? - Team Camaro Tech
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post #1 of 9 (permalink) Old Apr 20th, 01, 08:03 AM Thread Starter
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Is there a way to test if the power valve is good or bad in a Holley 600 (w/vacuum secondaries)? It's running very rich and it looks like raw fuel is comming out of the tailpipes when you leave it idleing in the driveway.The car had been backfiring through the carb before I adjusted the timing. No more backfires now and over all it is running OK but getting poor gas milage.This is a new carb (1 year old).
Any Holley experts in central Jersey?
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post #2 of 9 (permalink) Old Apr 20th, 01, 09:58 AM
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summit racing sells a tool for it kinda handy to keep around
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post #3 of 9 (permalink) Old Apr 20th, 01, 10:49 AM
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If there is fuel on the back side it is busted.

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post #4 of 9 (permalink) Old Apr 20th, 01, 04:39 PM
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Swipe a kid's rubber dart. Put the suction cup over the vaccum side of the valve and if the cup won't stay, it's shot.
You can also press the valve into the palm of your hand, press the plunger and then push, release the plunger and if it pops all the way out, it's bad. This second test is really hard to get a good seal on your hand, but I've done it, try it several times, if it works once, it's good.
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post #5 of 9 (permalink) Old Apr 21st, 01, 03:01 PM
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I use a Mityvac brake bleeder with the large rubber adapter end wetted with the power valve pressed against it. Then I create a vacuum and see if it holds.The mityvac isn't bad to own for brake bleeding anyway. Your carb is new enough it has the blow out protection although I don't know how bullet proof it is.Did this just start around the time of the backfires? My holley was doing that when I bought the car and it was from the float level being too high and the fuel pressure also too high.
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post #6 of 9 (permalink) Old Apr 22nd, 01, 07:03 PM
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[QUOTE]Originally posted by davidpozzi:
[B]Swipe a kid's rubber dart. Put the suction cup over the vaccum side of the valve and if the cup won't stay, it's shot.


I usually just put my lips on the back side and SUCK hard. (I think I start using the dart idea though) If you see spring colapse it is good. And if you are suckin air it is bad.
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post #7 of 9 (permalink) Old Apr 23rd, 01, 03:52 AM Thread Starter
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Thanks guys.. I'll be pulling the carb apart tomorrow. Have to borrow a vacuum guage to see if I need a different powervalve anyway. I've had the car about 2 months and I know the previous owner put in a new cam. I figure I'll check vacuum and make sure I know which valve to get in case the one installed is bad or the wrong size.
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post #8 of 9 (permalink) Old Apr 24th, 01, 02:22 AM
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I had the same problem with my 780 when I bought the car about a month ago. It was running very rich. My friend that rebuilt it said that when the car back fired that was what destroyed the power valves. I need to take the car to him this week and get some things adjusted on it because it has a slight hesitation each time I push down on the gas pedal and the 4 barrel doesn't come in just right.
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post #9 of 9 (permalink) Old Apr 26th, 01, 08:34 AM Thread Starter
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I got a new power valve and put it in. It was a real easy job...$10 for the power valve and gasket and 10 minutes under the hood. I'll fire it up tomorrow when I get the rest of the car back together and see what happens.
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