engine seems to stop reving for a moment

Old 10-06-2010, 09:59 PM
  #11  
cepx111
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Well chevyart, thanks for clearing that up, it makes more sense now.

I've also been thru the proform center section nightmare.

I installed one my son's 750DP, lets just say I caught hell getting that sucker dialed in, but I will say that once I did get it lined out, that car flys.

Their jet recommendation was WAY off for our combo, now I'm not saying that this is the case with yours but playing with the jetting wouldnt be a bad idea, it can be a cheap fix.

But on the power valve, why even bother?
If this is a race only car a power valve is useless, in a drag car your @ WOT 99.9 % of the time, the power valve circuit only comes into play at part throttle, it's just a transition circuit for driveability, not a tuning aide in a dragcar, plug that hole, jet the carb up and "square" and be done with it.

Goodluck>Cp
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Old 10-07-2010, 11:36 PM
  #12  
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hey cepx11 thanks for quick answer. stock 750 holley comes with 75 square with 2 power valves, so if i remove the front and rear power valves and step up 8 jet sizes (as recommended by holley and quick fuel), then i should start jetting at 83 front and rear. i got the carb from my buddy already done and i only made a few minor changes. he had it jetted 82 in the front and 84 in the rear.i changed back to a front power valve(3.5) and lowered front jets to 74s(down 8 sizes). i really thought that this would help prevent loading up whild driving in the pits. i asked on the forum about the power valve vs no power valve for drag only car and the views were about 50-50 for and against, so i felt the safest way was WITH the power valve in the front. does jetting sound right to you and i guess your thought is to NOT run a power valve. i really appreciate your input. i still have time to go NO POWER VALVE in front. im going racing on sunday thanks art
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Old 10-08-2010, 09:46 PM
  #13  
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Sorry for the delayed response, I work nights. :x

On your jetting, it's hard to say, every combo likes something different. But if I had to make a stab no knowing all your variables, I'd say 80 sqaure would not be a bad starting point.
It also depends on what your trying to accomplish, if speed and ET is all your after, being a tad fat is usually what your looking for, just jet it up till your MPH drops off and then go down 1-2 jets and lock it down.
But if your a bracket racer like me, lean is mean, I think my sons carb is jetted 72-73, no power valves, 50cc secondary accelerator pump.
It's a a failry mild 351W that runs 750's 1/8 low 11's 1/4 and yes it's a frigging ford.

Jetting can be a huge enigma to some folks, but really it's just something that needs to be played with in order to find out EXACTLY what the motor is asking for and what your trying to accomplish.

Gooluck and let us know how it pans out>Cp
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Old 10-09-2010, 04:04 AM
  #14  
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you are a good man cepx. im going to run car tomorrow. gonna start out with the same setup that i experienced my problem with and first watch the fuel pressure guage and then work from there.. this track is up over 1000 ft above sea level and last rrack was about around 300 ft abpve sea level, so i should go a tenth slower for starters over last track. ill let you know the results. thanks again art
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Old 10-09-2010, 11:10 AM
  #15  
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Originally Posted by chevyart
you are a good man cepx. im going to run car tomorrow. gonna start out with the same setup that i experienced my problem with and first watch the fuel pressure guage and then work from there.. this track is up over 1000 ft above sea level and last rrack was about around 300 ft abpve sea level, so i should go a tenth slower for starters over last track. ill let you know the results. thanks again art
Hey man, no problem, that's what we're here for, help.

I hope all goes well and you get that car dialed in and you go some rounds>goodluck<:wink:

Me and the boy are getting ready to head out right now, so wish us luck!



Cp
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Old 10-09-2010, 12:00 PM
  #16  
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hey cepx sounds like you got a nice family race team i like that. a family that races together stays together. good luck out there ill talk soon art
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Old 10-10-2010, 06:51 AM
  #17  
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i agree get rid of the power valves and step up the jet sizes :!: :!:
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Old 10-10-2010, 02:57 PM
  #18  
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Originally Posted by chevyart
hey cepx sounds like you got a nice family race team i like that. a family that races together stays together. good luck out there ill talk soon art
Well it definetly has its joys and woes.

I work on that damn ford more than I do my own car :x

I get to pull the trans again tomorrow, converter we put in it last week aint right, lucky me.......

How did it run today?

Cp
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Old 10-11-2010, 09:47 AM
  #19  
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hey cpx went to lebasnon valley(ny) yesterday. first pass dont even count. spun tires so bad i was embarresed. forgot to check air preszsure). 2nd pass was race time. car launched good and ran good but et was only 11.47 and mph was off by about 1-2 mph(lost race by 11 thousandths of a second) i let off just before end because i couldnt see the guy(didnt use my mirror and just looked to side.he caught me and i lost by maybe inches. they let me do a time trial and the car spun alot again(didnt care about that) and when i shifted around 7500 the car had like a bad miss(stutter) or something and it lasted for only a second. i checked the fuel pressure guage(in car) and it read 7 lbs(thats ok). car picked right back up but ran a loust 11.7 (60 ft tome was partially to blame for that. problem is that come and go miss ive been getting since switching carb . i really think it is the 3.5 power valve in there(too low a number), i am putting the vacum guage on there today.still havent seen the power valve that was in old carb, but it definitel the right number power vaLve.. and will try the power valve (the right size if the wrong one has been in there. if it was the right one in there then i will go to straight jets on front anbd rear and step the size up to 84 square.i worry about loading up in the pits, but quick fuel told me i could adjust the idle circuit air abeeds to lean out the idle circuit to help prevent loading in the pits. in my old cargb the power valve in there was definitely the right size. still trying to get the metering blocks off old carb. they are like welded onto the main body. ill keep you posted. any more suggestions ,i am listening thanks art
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Old 10-11-2010, 10:43 PM
  #20  
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Originally Posted by chevyart
hey cpx went to lebasnon valley(ny) yesterday. first pass dont even count. spun tires so bad i was embarresed. forgot to check air preszsure). 2nd pass was race time. car launched good and ran good but et was only 11.47 and mph was off by about 1-2 mph(lost race by 11 thousandths of a second) i let off just before end because i couldnt see the guy(didnt use my mirror and just looked to side.he caught me and i lost by maybe inches. they let me do a time trial and the car spun alot again(didnt care about that) and when i shifted around 7500 the car had like a bad miss(stutter) or something and it lasted for only a second. i checked the fuel pressure guage(in car) and it read 7 lbs(thats ok). car picked right back up but ran a loust 11.7 (60 ft tome was partially to blame for that. problem is that come and go miss ive been getting since switching carb . i really think it is the 3.5 power valve in there(too low a number), i am putting the vacum guage on there today.still havent seen the power valve that was in old carb, but it definitel the right number power vaLve.. and will try the power valve (the right size if the wrong one has been in there. if it was the right one in there then i will go to straight jets on front anbd rear and step the size up to 84 square.i worry about loading up in the pits, but quick fuel told me i could adjust the idle circuit air abeeds to lean out the idle circuit to help prevent loading in the pits. in my old cargb the power valve in there was definitely the right size. still trying to get the metering blocks off old carb. they are like welded onto the main body. ill keep you posted. any more suggestions ,i am listening thanks art
As far as the air pressure whoops, I aint never done that :roll: ...lol I think we all have, no biggie.
Damn ya'll only get one time trial? Whats up with that?
We usually get 3 for sure, sometimes 4 but I race at a laid back outlaw track in north mississippi, that would be in god's country if your wondering :wink:

Man I see your still stuck on them PV's, I'd loose them sum bitches before I did another thing to the carb, but 84 sqaure is wicked fat IMO for a 750cfm DP on a 350 anything. I'd go 80 sqaure and work my way up or down till it's dead nuts on.

Note:
As a comparrison I'm jetted 88 sqaure on my 1050 dominator which sits atop a 500CI bigblock.

Also, plugging them and squaring or not squaring up the jetting will NOT make it load up in the pits, that would be the idle circuit causing that problem, just lean that sucker out with a couple turns of the mixture screws (IN), if that dont do it, you got other problems, a BLOWN power valve comes to mind, another reason to loose them suckers.
In certain circumstances you have to add additional air to the idle circuit, a couple small 1/8 inch holes drilled in the primaries will take care of that with a quickness.

Ok, let me know what you decide to do and how it pans out.

Goodluck>Cp
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