power valve plug

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power valve plug

Post  johndickjr on July 21st 2013, 8:50 am

i decide to try something new and not run a power valve. i noticed now that when it look into carb and hit the gas it shoots fuel from the squirters like normal and also pulls fuel out of the boosters about a split sec after i hit it, is this normal, or maybe i should just go back to a PV, car idles at 4-5 inch of vacuum, and just excatly does a pv work, when the rpm is at say 3000 it has 12 inches of vacuum, at what point does vacuum start to go down to open the pv

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Re: power valve plug

Post  Dave C. on July 21st 2013, 12:17 pm

That's not much vacuum. Anyway, the PV will open when the vacuuum drops below the PV rating. The vacuum drops when the throttle blades open up.

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Re: power valve plug

Post  LivermoreDave on July 21st 2013, 12:27 pm

John I also have traveled the same path. First let me say, if a carburetor is built and adjusted correctly along with a good tune up, the power valve should give good service. I have modified carburetors to somewhat protect the power valve from a high pressure event and it does not always work.

I have recently removed the power valve and plugged the power valve position on a street driven work pickup. It has taken a bit of time to get it "workable" and a bit of change in driving habit. So far so good!

As to your question of "how does a power valve work" and vacuum questions. The power valve's value is rated in in.Hg (inches of vacuum). When the vacuum side of the power valve is exposed to a vacuum lower than the power valve value it begins to open and allow fuel from the carburetors fuel enrichment circuit to flow into the main well. The amount of fuel allowed into the main well is regulated by two things, the volume capacity of the power valve and the fuel enrichment passage manufactured into the carburetor. I have found that all fuel enrichment passages are not the same, possibly due to lack of manufacturing control. I too have found that altering the power valve enrichment passage can offer different results in the engine's tune up, good and bad depending on each tuner's preferences.

The power valve circuit vacuum is effected as soon as the throttle blades begin to open, lessening the vacuum available for the power valve to remain closed. As you posted to a high vacuum reading at a higher engine speed, engine demand and the vacuum reading are directly related. When the engine's demand for fuel (part throttle or closed throttle) is less (as the vacuum increases) the power valve will begin to and close at a vacuum level higher than the power valve's value.

Maybe not completely accurate, but close,
Dave.

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Re: power valve plug

Post  Dave C. on July 21st 2013, 4:57 pm

^^^^ What Dave said! I think. scratch 

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Re: power valve plug

Post  johndickjr on July 21st 2013, 5:10 pm

i was more worried about fuel coming out of the booster legs so early that i can see it

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Re: power valve plug

Post  Dave C. on July 22nd 2013, 3:46 am

John , fuel will flow through the boosters as the throttle opens .

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Re: power valve plug

Post  johndickjr on July 23rd 2013, 5:30 pm

i took it out and will put a 2.5 pv in it tomorrow, just don't seem near as responsive and as clear as when it had one in it, just bearly touch the throttle and gas pours into the motor


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Re: power valve plug

Post  Dave C. on July 23rd 2013, 5:49 pm

Is that the only change you made?

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Re: power valve plug

Post  LivermoreDave on July 23rd 2013, 6:53 pm

johndickjr wrote:i took it out and will put a 2.5 pv in it tomorrow, just don't seem near as responsive and as clear as when it had one in it, just bearly touch the throttle and gas pours into the motor

John I must ask a few stupid questions, so bare with me. As you described in your original post, you felt the carburetor was delivering too much fuel. Now to your recent post. You wrote;"i took it out", you did replace the power valve with a plug, correct? With the power valve enrichment circuit non-functional and main jet close to correct the engine should have exhibited a lean condition off idle. If the "gas pours into the motor" as you posted, you may need to look elsewhere within the carburetor for the problem. My opinion, remove the carburetor and rebuild it while looking for the problem.

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Re: power valve plug

Post  kim on July 23rd 2013, 9:13 pm

Just taking it out, without a plug, its going to really be rich, as the surface area will be open all the time.

Taking it out with a plug, idle should remain the same, light throttle cruise will be richer, as you should have increased jet surface area by 6 jet sizes to compensate for WOT performance with the power valve. The intermediate throttle positions will run richer without the power valve.

With a proper rated power valve, the valve is closed and part throttle driveableity will be leaner, cleaner, and throttle response crisper. The power valve should only be opening at nearly WOT demand.

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Re: power valve plug

Post  LivermoreDave on July 24th 2013, 10:09 am

LivermoreDave wrote:
johndickjr wrote:i took it out and will put a 2.5 pv in it tomorrow, just don't seem near as responsive and as clear as when it had one in it, just bearly touch the throttle and gas pours into the motor

John I must ask a few stupid questions, so bare with me. As you described in your original post, you felt the carburetor was delivering too much fuel. Now to your recent post. You wrote;"i took it out", you did replace the power valve with a plug, correct? With the power valve enrichment circuit non-functional and main jet close to correct the engine should have exhibited a lean condition off idle. If the "gas pours into the motor" as you posted, you may need to look elsewhere within the carburetor for the problem. My opinion, remove the carburetor and rebuild it while looking for the problem.

Dave.

I may have made a mistake writing the above highlighted words. The definition of my words were. main jetting at factory specifications with a power valve installed. I was assuming as the original poster wrote, the power valve was the ONLY change, therefore with the power valve removed and main jetting not adjusted the air fuel ratio off idle and during light, part or WOT throttle, the mixture would be lean or leaner than the original poster described.

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Re: power valve plug

Post  johndickjr on July 24th 2013, 9:15 pm

went ahead and put a 2.5 pv back in, took carb apart cleaned it, checked it all out, put it back on car, readjusted base idle and 4 corner mixture, going to tnt friday , ill see what new cam..intake and carb does, im thinking 11.70 range

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Re: power valve plug

Post  LivermoreDave on July 24th 2013, 9:34 pm

John after the rebuild did the carburetor/engine act normal? Good luck on the upcoming test and tune.

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Re: power valve plug

Post  Dave C. on August 7th 2013, 6:48 am

How did the carb do ?

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