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Author Topic:   power valve or plug
posted June 19, 2003 09:07 AM
Eliminating the PV is the wrong thing to do. The carb can then only be jetted properly for either wide open throttle, and will only function right during rpm ranges where the PV circuit wouldn't be other words, it is NOT the answer and is an "old school" crutch. We don't recommend doing it.
As for choosing the correct power valve, it is done by getting a vacuum reading at idle (of full manifold vacuum, not part-throttle vacuum) and choose the PV that is about 2 sizes below what you have for inches of vacuum.
In other words, if you have 8"HG+ of vacuum, you would run a 6.5 power valve, if you had about 6" of vacuum, run about a 4.5 or so, etc...

Hope that helps.

Kinetic Performance

posted June 19, 2003 02:48 PM
What about plugging the secondary side but running a powervalve on the primary side? 750 Holley dp on gasoline. Any advice?

posted June 19, 2003 03:04 PM
That's a horse of a different color. The 650 and some 750's and 850's (4776,4777 and 4780, if memory serves) came like that from the factory.
The point is, at least there is ONE operating power valve circuit.
And the same rules for choosing the right PV still apply.
The thing to do is to install the easily obtainable power valve blowout protection kit (check ball, spring and washer) and a new PV and the problem is solved.

Hope that helps,


posted June 19, 2003 09:14 PM
KPLUGNUT will this work on a motorcraft 2-barrel? Post is above in ministock tech. We blew out a power valve and are running a plug with # 51 ford jets. Motor is stock with header, fuel inj. intake homemade one inch spacer and carb is small 1.08 2-barrel. Pump arm is in top of four holes. Motor when warm will idle and surge up and down 300-500 rpm. Please Help BIGG C

rico 08
posted June 19, 2003 09:37 PM
If you're concerned about blowing power valves drill out the power valve hole to accept a check ball and stake it in the hole that way it won't fall out,with that in place it will seat when the engine backfires and will save the power valve,KP has probably done this mod.

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