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Side effect of removing a power valve from carb ? #750409 07/17/10 01:25 PM 07/17/10 01:25 PM
Joined: May 2005 Posts: 581 Texas Texican OP mopar
Texican OP mopar Joined: May 2005 Posts: 581 Texas	(First of all, I didn't remove it...) I have a 340 +6 (AAR Cuda) Note: I have a big cam with long duration.... and have virtually no vacuum at idle (9") It was originally running very very rich and fouling out plugs within minutes... My guess is that I had the wrong size PV...and was open at idle. A friend of mine looked at the center carb, and said I should remove the PV....and he replaced it with a block off.... He then upjetted to compensate for the lack of the power valve.... That actually fixed the problem of running Rich and fouling plugs, but here's my current problem...which I think may be the side effect of a missing power valve. Sluggish off the line Backfires and pops under heavy acceleration (usually means LEAN mixture) Runs ok after a few seconds of full throttle...but still a few pops... My theory is that I need a (4") PV (half of vacuum reading at idle), but here are my questions: 1.) What is the side effect of having it blocked off ? 2.) How much fuel (percentage) does the PV add under full throttle ? (10% - 30%) etc..? My timing is set at 20/36 and all in at 2500... (probably a little early) ? Thanks for any advice. Im all ears.

Re: Side effect of removing a power valve from carb ? [Re: Texican] #750410 07/17/10 02:29 PM 07/17/10 02:29 PM
Joined: Jan 2007 Posts: 3,695 nc E emarine01 master
emarine01 master E Joined: Jan 2007 Posts: 3,695 nc	I am no expert on carbs so that being said heres my We had the same problem on a bg 850 when removing the front pv, we changed the squirter up a couple of #s and fixed a stumble on hard excell, I could be totaly wrong now but no one else is kickin in, good luck

Re: Side effect of removing a power valve from carb ? [Re: emarine01] #750411 07/17/10 02:38 PM 07/17/10 02:38 PM
Joined: May 2005 Posts: 581 Texas Texican OP mopar
Texican OP mopar Joined: May 2005 Posts: 581 Texas	Well, from a dead stop, when I accelerate hard off the line it stumbles...bogs...and pops/backfires... Was thinking its a little lean. When outboard carbs kick in it does a little better but stll not 100. Anything past 3500 RPM...the cam comes alive and outboard carbs start working and it's ok. Diff: 3.55:1 Tranny: 4-speed

Re: Side effect of removing a power valve from carb ? DELETED [Re: Texican] #750412 07/17/10 06:45 PM 07/17/10 06:45 PM
Joined: Oct 2007 Posts: 4,210 New York polyspheric master
polyspheric master Joined: Oct 2007 Posts: 4,210 New York	Post deleted by polyspheric Boffin Emeritus

383man [Re: polyspheric] #750413 07/17/10 06:59 PM 07/17/10 06:59 PM
Joined: Jan 2003 Posts: 27,421 Balt. Md 3 383man Too Many Posts
383man Too Many Posts 3 Joined: Jan 2003 Posts: 27,421 Balt. Md	Quote: Your original problem was that the primary throttle was too far open at idle, which exposed the PV to vacuum. Fix that first. The P/V has manifold vacum all the time even at idle. Usually the problem is that the idle gets turned up with the large duration cam and exsposes the transfer slots. And then the tuner leans out the idle circuit trying to clean up the idle and now when you step on the gas you dont get the extra fuel from the transfer slots. Ron

Re: Side effect of removing a power valve from carb ? [Re: Texican] #750414 07/17/10 08:02 PM 07/17/10 08:02 PM
Joined: Jan 2003 Posts: 31,061 Oregon A AndyF I Win
AndyF I Win A Joined: Jan 2003 Posts: 31,061 Oregon	The power valve probably wasn't the problem as it only adds extra fuel to the main circuit. At idle, it shouldn't really change the mixture much if any at all. For a street car you should do everything possible to keep a power valve in the carb. That way you keep the main circuit lean at cruise and then have the power valve to add fuel at WOT.

Re: 383man [Re: 383man] #750415 07/17/10 09:03 PM 07/17/10 09:03 PM
Joined: Jan 2003 Posts: 10,015 Frostbitefalls MN (Rocky&Bullw... gregsdart I Live Here
gregsdart I Live Here Joined: Jan 2003 Posts: 10,015 Frostbitefalls MN (Rocky&Bullw...	Quote: Quote: Your original problem was that the primary throttle was too far open at idle, which exposed the PV to vacuum. Fix that first. The P/V has manifold vacum all the time even at idle. Usually the problem is that the idle gets turned up with the large duration cam and exsposes the transfer slots. And then the tuner leans out the idle circuit trying to clean up the idle and now when you step on the gas you dont get the extra fuel from the transfer slots. Ron The fix is to set the throttle blades open a small amount for fuel, so .050 of the transfer slot shows, no more? Some one will chime in and come up with the right specs. Then, drill holes in each primary throttle blade to feed it the air it wants. Try 1/8 to start, and see how much your idle improves over the start point, which is probably no idle at all. Move up in hole size very slowly till you hit the right rpm hot. Reset your accelerater pumps to add fuel till it will leave hard, jet for mph, and you have it. Someone with 6pak experiance may be able to give you info on whether you need to add holes in the end carbs, but without first hand knowledge, I wouldn't do it till you run out of options trying to lean the idle. 8..603 156 mph best, 2905 lbs 549, indy 572-13, alky

Re: 383man [Re: gregsdart] #750416 07/17/10 09:49 PM 07/17/10 09:49 PM
Joined: May 2005 Posts: 581 Texas Texican OP mopar
Texican OP mopar Joined: May 2005 Posts: 581 Texas	Great feedback, thanks! Question: approx how much fuel does a PV add at wot over just the primary jets... Compared to a carb without a pv ? My idle vacuum is about 9". Should I install a 4" pv ? Thx

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