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Thread: 750 Holley HO carb air gap intake ?

  1. #1
    Senior Member SENIOR BUILDER
    Join Date
    Apr 2007
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    105

    750 Holley HO carb air gap intake ?

    I was running a performer intake with a stock quadrajet..car was pretty consistent for brackets..I mounted a rpm air gap with a AED holley 750 dbl pump carb 73 primaries 80 seconds..Primaries has a 4.5 power valve the secondaries has no power valve...

    Et's are better in the heat than cool air..I would think my et's across the board would be better in the night air but only gets worst as the night progress.Even after a 45 min cool off time in the night air still a loss in performance.

    I am trying to set this car up for bracket racing.NO can do when my et's are all over the place..I am pretty consistent on my rt's time slip shows the car has taken a fall in performance in the cool air.Could I be a over jetted? Heat or cool night air car doesnt pull as it should on the upshift..

    With the performer intake stock quad upshift in the 8th was I would say 2 seconds before the stripe..Yea some tall gears.Now with the air gap and holley I am in second gear a good 4 1/2 to 5 seconds before the stripe..Performance has improved but stumped on the loss of power in the cool air..

    Any help well appreciated thanks..

  2. #2
    Senior Member DYNO OPERATOR
    Join Date
    Aug 2007
    Location
    Lost Creek, WV
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    533
    There are a few things you need to look at. I would check your float level, then check fuel pressure. Then take a look at your spark plugs. It sounds like you are a little on the lean side.

    TS1955

  3. #3
    Senior Member SENIOR BUILDER
    Join Date
    Apr 2007
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    105
    Float level is in the mid of sight plugs front and rear..The carb was purchased with 83 secondary jets..Ran it a few times and checked plugs with the 83's..Plugs were fouled out bad.I did replace plugs with NGK's and re jetted the secondaries with 80's..I will take a look at the new plugs to see if still running to rich or possibly lean.The engines seemed to perform better with the 80's..Fuel pressure is on a stock mechanical pump rated at 6.5..

    Sbc edlebrock performer heads,full rollers 1.5's,RV cam,RPM air gap,AED 750 dbl pumper,hooker long tubes,flow masters...<<<< Some of the pieces to my puzzle.. Engine has under 8000 miles on it fairly fresh.Thanks for your reply..

  4. #4
    Junior Member SHOW GUEST
    Join Date
    Feb 2005
    Posts
    1
    Fuel level should barely trickle out of the plug holes with the plug out, sounds like they are too high. Doesn't explain your problem though, which is strange. Plugs don't explain it, nor does fuel pressure as it should be the same day or night. I run a 750 on my Air Gap but I run thru a cool can so fuel is always the same temp an no problems. Your issue sounds like it may be humidity related. Tune your carb with a vac gauge attached to the manifold. Adjust the mix screws until you obtain the highest vac rating at idle. Beyond that I have no other ideas to offer for this weird issue. Most engines run better in cooler air.

  5. #5
    Senior Member SENIOR BUILDER
    Join Date
    Apr 2007
    Posts
    105
    I believe I figured this out with the aid of another member who use to visit RJ..I run a 1 inch spacer with a vac line for my pcv..I am going to install a header evac system soon..

    I plugged the vac line to the spacer and pulled my pcv valve for time trials last week..First pass beat my personal best et ever..I waited for some cool night air..Beat that personal best as well..

    Car 60'd better and all across the board and gained 1 1/2 mphrs..I believe that hot crankcase vapor being pulled in through the spacer vacum port was defeating the purpose of the air gap ect..I did not touch a thing from my last visit to the track other than the pcv and spacer vac port.

    Thanks


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