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  #1  
Old 09-20-2001, 04:39 PM
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Hammer 74 Hammer 74 is offline
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Question Blown Power Valve

Is a blown power valve going to effect idle? I would think it would only effect the primary circuit because it is seperate from the idle circuit. I dont know.
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Old 09-20-2001, 08:50 PM
shawnronan shawnronan is offline
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The power valve is designed to enrichen the main metering during acceleration. When the throttles open up, manifold vacuum is lost. Vacuum holds the valve closed until it drops below a certain value and begins to open. To answer your question, the idle circuit is seperate from the main metering circuit and will not be affected by the power valve.
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Old 09-20-2001, 11:09 PM
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amoparguy amoparguy is offline
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shawnronan did a nice job explaining how power valves work BUT....they can have an effect on idle if the power valves rating is higher than manifold vacuum @ idle. Using a Holley carb as an example, if the carb has a 65 powervalve (6.5 in/hg) and manifold vacuum is low at idle (below 6.5 in/hg) due to a long duration cam the power valve may open or flutter and enrich the air fuel mixture. A blown powervalve will also effect idle. You'll know if it happens, the exhaust fumes will smell exrtemely rich and it'll burn your eyes.
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Old 09-20-2001, 11:26 PM
shawnronan shawnronan is offline
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I guess if you think about it, a blown power valve would be stuck open thus affecting everything, thanks for the correction!!. P.S. buy the Holley reusable (blue) gaskets and change that sucker!!
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Old 09-21-2001, 11:19 AM
T748 T748 is offline
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I thought that with a blown power valve the diaphram is ruptured sending the fuel thats on one side of the diaphram into the non fuel side (the side that sees the vacuum signal).Then raw fuel is being drawn into the powervalve vacuum port and down into the motor.I'm no holley guru,correct me if i'm wrong on this one. -Tom.
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Old 09-21-2001, 11:32 AM
beepbeepsrule beepbeepsrule is offline
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T748, you are correct. A power valve with a ruptured diaphragm lets the engine draw fuel right from the bowl. So, if the term "blown power valve" means a leaking diaphragm then the mix will be rich all the time at any rpm.
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Old 10-02-2001, 09:25 AM
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Default Power Valve

Will backfire through the carb damage or blowout a power valve?
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Old 10-02-2001, 02:30 PM
beepbeepsrule beepbeepsrule is offline
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Yup.
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Old 10-02-2001, 09:42 PM
Toddd Toddd is offline
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Question How can you tell a power valve is faulty?

Upon visual inspection...how can you tell a faulty power valve from a good one?. I've really had some bad luck with my Holley 750 vac sec. I have a "Good friend" who lent me his Thermo- quad, and the car really responded. There is some thing really wrong with my Holley carb too. thanks for the info.
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Old 10-03-2001, 12:01 AM
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When any holley sits around for more than 6 mos its starts to build up varnish and crap in the metering block which will make it totally misbehave and soaking it in carb cleaner doesnt always help as those internal passages have 90* bends and are very very small,after ebuilding if you still have probs replacing the metering block is a good idea and will remedy 90% of your probs.last time I bought one it cost $38..........PRO.....
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Old 10-04-2001, 01:42 AM
shawnronan shawnronan is offline
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I always blow compressed air through all the passages when it is just out of the cleaner. It has always worked well for me and I've dealt with some pretty crusty looking units. I agree that when they sit too long they go bad, the power valves tend to dry rot! It would be preferable to drain the fuel if it is going to sit for any length of time.
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Old 10-04-2001, 02:42 AM
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Thanks for all the input on the power valve issue. I have had problems with metering blocks like PRO said. Changed it out and ran good. Its allways good to have a bunch or spare Holleys around.
The power valve looked good but it still gushed fuel out at part throttle with no load on it. Its not my car but am helping him find the cause. Thanks again.
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