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power valve

Old 07-13-2021, 05:03 PM
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Talking power valve

posted before about power valves etc,,thanks for advice

now i know i have 15 inch of vacum at idle,,,not in water , but in driveway..
so i should get 70-80 power valve for primiary side...??
what should knock jets down too??..82 ---84 ..again primiary side.

carbs are 1050,,3 circuits,,,,both power valves blocked,,92 jets all around.
issue is motors are running fat....547's.
yes i know i need to check plugs at idle,,,then mid range check,,then a hard run and check
but trying to get started...

thanks for advice........
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Old 07-14-2021, 12:47 AM
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Jetting and PV's have nothing to do with being rich at idle. Engines need to be run under load to determine if jetting or PV changes are needed.

If you wanted to install a PV in the primary, a 6.5 is pretty standard, then reduce primary jetting to the 84 range.
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Old 07-14-2021, 06:59 AM
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Originally Posted by Griff View Post
Jetting and PV's have nothing to do with being rich at idle. Engines need to be run under load to determine if jetting or PV changes are needed.

If you wanted to install a PV in the primary, a 6.5 is pretty standard, then reduce primary jetting to the 84 range.
ok thanks griff,,,,,just want get going on this...i know i will have to run boat ,,,kill motors ,,look at plugs..

thanks....................
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Old 07-14-2021, 08:56 AM
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Before you change power valves I would keep the vacuum gauge hooked up and record the readings through the entire rpm range idling and under load in the water.
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Old 07-14-2021, 11:50 AM
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Originally Posted by flashgordon View Post
ok thanks griff,,,,,just want get going on this...i know i will have to run boat ,,,kill motors ,,look at plugs..

thanks....................
I'd get the idle cleaned up first so it's not making plugs hard to read when water testing. You'll be far and away more able to tune it if you can get an O2 sensor and A/F ratio meter on it.
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Old 07-16-2021, 10:41 AM
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Originally Posted by TomZ View Post
I'd get the idle cleaned up first so it's not making plugs hard to read when water testing. You'll be far and away more able to tune it if you can get an O2 sensor and A/F ratio meter on it.
was going to put o2 sensors on,,,but my extensions from headers are wet...would be big job to change was suggested to put in 90 degree adapter for sensor,,,just not thru all that right now...thanks for advice...

and i was planning on taking vacum guage out with me on next run,,,look at numbers mid range etc....maybe i would be better just jetting primary down..??
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Old 07-16-2021, 11:22 AM
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90* adapters are screw in. No big deal to install.
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Old 07-25-2021, 11:11 AM
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Originally Posted by GLENAMY 242SS View Post
90* adapters are screw in. No big deal to install.
well i would have to remove my extensions,,meaning remove tips from transom to get out my extensions...then get bung welded into my extensions,,then reassemble....fun...think we chatted on this before the 90 degree adapters..
thanks.............
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Old 07-25-2021, 07:09 PM
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If you`re rich why would you add an unmetered fuel fill to your carbs?
Whomever had no power valves in there had it right.
Powervalves belong in cars not boats
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Old 07-26-2021, 10:16 AM
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Edit: OP said he's got rich looking plugs. He didn't say at idle.

Don't add in the variable of power valve unless you take out even more from primary, and perhaps secondary too.
Power valves add 6 to 8 numbers to the fuel at whatever vacuum you put in the block. So if it's rich with 92's start by taking out some jet. Like 10 or more primary, and 2 or 4 secondary.

I think he wanted to lean out the primary side jetting so the PVs only add fuel below their rated vacuum. If I understand things, that gets him more flexibility through the mid range.

Really needs AFR gauge. Best $ you can spend.

I am learning/fighting this myself right now. Got a lean spot just before (mechanical) secondaries open on mine. oops, don't answer- No Hijacks!

Last edited by NHGuy; 07-27-2021 at 05:39 AM.
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