Symptoms of blown power valve - Chevelle Tech
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post #1 of 8 (permalink) Old May 4th, 10, 8:25 PM Thread Starter
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Symptoms of blown power valve

468 Big block with a 4150HP / 950 cfm Holley was running very rich could not get to idle, them it developed a pop pop pop like a carb back fire. Could this be a blown power valve????

Tried to look at some old posts but could not find what I was looking for!!!
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post #2 of 8 (permalink) Old May 4th, 10, 10:19 PM
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Re: Symptoms of blown power valve

A blown power valve will make the engine very rich at idle and adjusting the idle mixture screws will probably make no difference in the idle speed. Have never had a blown power valve cause popping though, could be that you have other problems too.

Bill
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post #3 of 8 (permalink) Old May 4th, 10, 10:46 PM
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Re: Symptoms of blown power valve

I had the power valve in my 850 cfm double pumper go out twice. Each time it would barely start and wouldn't idle. I got it home by never letting the rpms get below about 1500. Finally changed out to a power valve made for a car running alcohol and that was 2.5 years ago.

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post #4 of 8 (permalink) Old May 4th, 10, 10:52 PM
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Re: Symptoms of blown power valve

popping is basically never caused by the carb unless you're talking about a cold backfire.

Need to start checking around your distributor and other ignition stuff.

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post #5 of 8 (permalink) Old May 4th, 10, 11:34 PM Thread Starter
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Re: Symptoms of blown power valve

Well maybe it wasn't a pop, more like a crack. The motor was running rich and started to load up increasing the rpm. Then I cracked the throttle and when the rpm came down it just started making a pop / cracking sound. Now it starts hard and has that sound, when I accelerate. I was thinking power valve because before it was impossible to set idle and ran very rich.
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post #6 of 8 (permalink) Old May 5th, 10, 8:53 AM
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Bill R
 
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Re: Symptoms of blown power valve

A blown power valve usually won't cause a hard start problem, nor any unusual sounds. I think your problem is something other than power valve.

Bill
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post #7 of 8 (permalink) Old May 5th, 10, 9:27 AM
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Re: Symptoms of blown power valve

A blown power valve will let fuel directly into the intake manifold through the vacuum passage that operates it.

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post #8 of 8 (permalink) Old May 5th, 10, 1:39 PM Thread Starter
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Re: Symptoms of blown power valve

Man o man due I feel like a dork!!!!!!!

I set the valves the other night and then started tuning on the carb.

Thinking that everything I touch is golden (not) and the valve timing shouldn't be an issue.

After reading the posts you guys put up got me thinking. Couldn't sleep so got up @ 5am pulled the rocker covers off and guess what? Found # 5 was loose as goose. It must have backed off or I didn't tighten it properly.

Anyways is all good now guys thanks. I'm off to live another day.


Again big thanks to you all. Sometimes all a guy needs is a little nudge in the right direction. The power valve was shot as well LOL.

Thanks Big Earl
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