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well if you have a PV in both the pri and sec. side and you plug them both...yes, you'll probably have to increase your jet size. How much depends on what size the PVCRs are (power valve channel restrictions)...but you can safely ASSume that an increase of 10 jet sizes will get you really close.
 

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8-10 numbers. if had 72 in front, go 80 or 82. might need to restrict the idle circuit to get back the needle adjustment. mr gasket used to make a neat plate kit to do that.
 

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You want to do this... why?

The whole idea of the PV is to give it extra fuel just when it needs it. To have it jetted up not to bog would make it pig-rich at almost any other speed, I'd think. Foul plugs, wash the cylinders, burn your eyes, down on power.

Good luck...
 

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Depends on the engine 3-5 has worked for me in the past. You can leave the primary PV in and just plug the secondary.
 

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Discussion Starter · #8 ·
Just have it in the front. It is a street/strip. I have got the lowest one in and if you bring the throttle just past idle, it just dumps in the fuel. You can watch it. Can't stand to be around it it's so rich. 4-5 mpg. Most people tell me to remove it.
 

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I think you have something else going on if you get fuel pullover on the mains with just cracking the throttle open. What's your manifold vacuum? Check your metering blocks, idle and high speed air bleeds for restrictions.
 

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Discussion Starter · #10 ·
There an easy way to explain which holes are the idle and high speed air bleeds?? I'll have to check them out again.
There any way to get a hold of, I think it is "biggs carburetors"?
_________________
1970 Mach 1
mild 408 [email protected]
519 fwhp, 532 ft.lbs torque
70 Tubbed, narrowed fastback
351C no #'s YET!

<font size=-1>[ This Message was edited by: jasonn on 4/11/06 11:59pm ]</font>
 

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removing the power valve will just make it even richer, especially at part throttle under a little bit of load.

the PV opens at a certain vacuum reading, usually a 3.5 PV opens at 3.5 in. Hg. So, if you're cruising along with very little load (flat ground not accelerating) the PV is closed and you're running on the idle circuit and to an extent the main jet. Normally if you have a really rich problem at part throttle, reducing the main jet size will help.

Occasionally, you'll get into a carb that simply will not let you jet it down far enough for satisfactory economy, yet still be able to supply the right amount of fuel under WOT. In this case, you can reduce the jet size until you get a little bit of a surge while cruising at low load, then drill out the PVCRs until you get your WOT mixture just right. Some metering blocks have adjustable PVCR's in them...which is basically 2 little mikuni style jets screwed in behind the PV. Once you get the cruise mixture pretty close, you can play with timing. Backing the timing down a little bit at a time until the surge goes away, then lean it out a little more...and soon you'll get to a point where you can't get rid of the surge, either that or it'll feel lazy. That's where you stop. I used this method a while back...used a custom built 950 HP on a mild 302 (I already had the carb) in my '84 GT...and got over 30 mpg day in and day out.

Air bleeds...the High speeds are the inner ones, the low speeds are the outer ones.
 

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Jason,

I have a Bigs 650DP that dumps so much fuel you can hear the engine gurgle up in the stands when I hit the throttle. I've talked to Jessie about it but couldn't resolve issue, so I parked it on the shelf. Jessie is a great guy and does good work so no one should take this as flaming him, because I'm not. I went down the same road thinking that I'd plug the power valve etc. to try to cure issue, but because I did not know each and every mod. he made, I changed my mind and started over with a different carb. It sounds like yours may be like mine.
 
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