Holley poping with new power valve???? - Team Camaro Tech
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post #1 of 3 (permalink) Old Jan 29th, 02, 01:55 AM Thread Starter
Senior Tech
Join Date: Apr 2001
Location: Newark, Ohio
Posts: 706

I just put a new 750 Holley Double pumper on my car and replaced the 650. I used the 4.5 power valve from the 650 and now the engine seems to surge while cruising and pops just off idle if i goose it. I did a vacumm test at idle in gear and only get around 6 inches of vacumm. I get 9 inches in park. Where do i start to begin, could it just be a vacumm leak somewhere. The car ran fine before I put the 4.5 power valve in the carb, I just put it in there because I was told to start with what I had before in the 650 carb. I turn the idle screws all the way and vacumm actually goes up and the engine doesn't stall like it is suppossed too. Thanks, Erik

68 Camaro RS, Built 355, 274 Comp Cam, Sportsman II Heads 200 c.c. 2.02. Ported to Performer RPM Manifold and 1.75" Headers, 1.5 Roller Rockers, 650 Holley, Steel Crank, 4.11 Gears but no posi yet! TH350 tranny w/ shift kit.
Erik Beckett is offline  
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post #2 of 3 (permalink) Old Jan 29th, 02, 06:32 AM
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Join Date: Apr 2000
Location: holliston, mass
Posts: 622

holley 0-4777 calls for a 125-65 out of the box (opens at 6.5")
this is the same power valve that comes stock in the 4779 as well (750)

Just for kicks, try bumping up the timing a bit.. and recheck the vacuum

Check back,

We're all glad to help

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post #3 of 3 (permalink) Old Jan 30th, 02, 03:38 AM
Join Date: Jan 2000
Posts: 208

If you have the transfer slot exposed more than about .040 you need to open the secondarys. Once you get that done try adjusting the idle mixture screws for the highest vacuum. If this works and you still have the popping try bumping up the jetting in the primary. Does it have a bog or lag, if so it is possibly to lean. I had this same type of problem on my BB and it was too lean in the primary. I went back to stock 80 jetting on 850 dp. This cured most of it and fixed the bog. Next get the pump cam assortment. I think i used the blue one that is almost triangular. The green is the same shape, but a bigger shot. It seems to give a faster initial shot to eliminate the lean condition off idle.

67 SS 427
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