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 Post subject: Power valve elimination
 Post Posted: Tue Apr 10, 2012 7:05 pm 
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Hello all
I've read many of the carb issue threads that relate to the removal of the power valves for racing, but am wondering what the drawbacks are for street/strip use? Is it driveability or fuel economy that suffers? What is the power valve actually doing?
Thanks
Jim


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 Post Posted: Tue Apr 10, 2012 11:37 pm 
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Unless your engine produces no vacuum it is unwise to remove an entire circuit of fuel from the curve.

The powervalve provides a circuit of fuel during the most critical time...under a load.


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 Post Posted: Wed Apr 11, 2012 12:23 am 
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Thank you Shaker
I appreciate the reply
Jim


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 Post Posted: Wed Apr 11, 2012 7:16 am 
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When one eliminates that PV circuit then MJ size will have to go up an average of 10 numbers or so, ie, say 74 with a PV and 84 without so fuel supply is not taken away, it's just that more of it is made available at smaller throttle openings and tends make for a richer mix at part throttle.

It's been my experience that a PV is not necessary on a race only application but they work well for the primary side only of any carb that's street driven.

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 Post Posted: Wed Apr 11, 2012 3:07 pm 
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Ken0069 wrote:
When one eliminates that PV circuit then MJ size will have to go up an average of 10 numbers or so, ie, say 74 with a PV and 84

My experience has been about 6 or 7 numbers.


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 Post Posted: Wed Apr 11, 2012 5:05 pm 
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J_6961 wrote:
Ken0069 wrote:
When one eliminates that PV circuit then MJ size will have to go up an average of 10 numbers or so, ie, say 74 with a PV and 84

My experience has been about 6 or 7 numbers.


Yeah, that may be the case as I just chose a random number for illustration purposes but there won't likely be any two carburetors that are the same. If memory serves my Dominator is 5 numbers less in the front with a PV.

I've found it's a bunch easier to get the tuneup right without PVs in most anything by jetting the same on all four corners and looking at time slips and or plugs if you know how to read them. Then if you want to run a PV you have something to work back to, ie, if you got time slips or an O2 setup then when you do us a PV you have those to help get the MJ where it needs to be.

I've beat my brains out (didn't take long) trying to figure how to use area of the orifices in the PVCRs to tell what jet is required both with and without a PV but the formulas just don't play out and the "W A G" factor seems to work about as well as anything for a starting point.

Your mileage may vary! ;-)

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 Post Posted: Wed Apr 11, 2012 11:14 pm 
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Agreed \:D/


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 Post Posted: Fri Apr 13, 2012 3:04 pm 
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I thank all you guys for the answers that you mentioned re Power valves. The real reason I asked is that the old carbs I'm using do not have NEW replacement valves available for them. This is essentially a street driven vehicle.
I'll continue to screw around with what I've got, and start a new thread on my next issue

Thanks again
Jim


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