Power valves in a blown gas combo
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Power valves in a blown gas combo

  1. #1
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    Default Power valves in a blown gas combo

    I run a 565/14-71 combo on pump gas in my jet boat and currious if anyone else runs power valves or what others run? Two 1250 dominators for carbs with 4.5 power valves in both primaries and secondaries, 94 and 96 for jets. The plugs are autolight ar3932 and are always black and sooty looking, never clean and slight brown. Seems to me that the power valves open on every surge and the vaccume bounces from 10 to 0.... It crusies down the lake at 6 inches of vaccume around 2700 rpm. or right at 0 vaccume around 3800.

    I am thinking of blocking off the power valves.

    Any input would be great!!

    Thanks

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    gn7
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    First, I am going to assume that the PVs are manifold referenced. If not, they are never opening anyways, might as well plug them. If they are manifold referenced and the MAJORITY of your time is spent wit the manifold is 4.5 or lower, you might as well plug them.
    PVs are not effected by surging, and SHOULDN'T put add any fuel while idling. PVs add fuel the main system ONLY, and add nothing to the idle/transition circuit. If they do you have other issue.

    If your running that rich now, I would plug the PVs and run you current jetting. Its sounds pretty close as is with out the PVs. It will be close enough to at least get a plug reading.

    3932 are a little cold for a lake boat with alum heads



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    Quote Originally Posted by gn7 View Post
    First, I am going to assume that the PVs are manifold referenced. If not, they are never opening anyways, might as well plug them. If they are manifold referenced and the MAJORITY of your time is spent wit the manifold is 4.5 or lower, you might as well plug them.
    PVs are not effected by surging, and SHOULDN'T put add any fuel while idling. PVs add fuel the main system ONLY, and add nothing to the idle/transition circuit. If they do you have other issue.

    If your running that rich now, I would plug the PVs and run you current jetting. Its sounds pretty close as is with out the PVs. It will be close enough to at least get a plug reading.

    3932 are a little cold for a lake boat with alum heads
    Thanks for the reply!! I think I will block them off and see how it goes from there for a start.

    What would you reccomend for plugs? Just go one step hotter? This set up sees 9 to 12 lbs of boost

    Thanks

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    gn7
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    When you get a handle on the jetting, you can get away with the primaries having a couple jet sizes smaller like it is now, but don't get much further than that apart, if the carbs are progeressive secondaries. If the carbs open the sec and the pri's together, jet it square.

    My favorite plug to get a reading from is an NGK 8. I can't give you a NGK 4554 which isin NGK's 8 heat range. They color up fast and easy to get a heat and timing reading from. I used to tune with them and switch to a #9 for racing. I stopped doing that a couple years ago and have never had any problems with them at all. I am a firm believer in running the hottest plug you can run the doesn't over heat. Many go with the coldest plug that doesn't foul. I used to believe that, but not any more.



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    Quote Originally Posted by gn7 View Post
    When you get a handle on the jetting, you can get away with the primaries having a couple jet sizes smaller like it is now, but don't get much further than that apart, if the carbs are progeressive secondaries. If the carbs open the sec and the pri's together, jet it square.

    My favorite plug to get a reading from is an NGK 8. I can't give you a NGK 4554 which isin NGK's 8 heat range. They color up fast and easy to get a heat and timing reading from. I used to tune with them and switch to a #9 for racing. I stopped doing that a couple years ago and have never had any problems with them at all. I am a firm believer in running the hottest plug you can run the doesn't over heat. Many go with the coldest plug that doesn't foul. I used to believe that, but not any more.
    Thanks for the advice!! I have a set of ar3933's in the shop I will give a try along with the power valves being pluged.

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