Results 1 to 9 of 9

Thread: boosters working early

  1. #1
    Senior Member MASTER BUILDER
    Join Date
    Mar 2008
    Posts
    173

    boosters working early

    been racing my car for 15 years and ran fine. just happened to look at the carb one day at idle (about 1200 RPMS) and noticed a steady stream running out of the boosters( NOT a little mist) ii i thought this shouldnt be happening. rebuilt the casrb and still get same stream at high idle. put on a new 750 with a race center section and still get the same gas running at high idle car only has a vacum reading of about 5-6 inches of vacum at idle(in gear) tried a 6.5 power valve in front and also tried a 4.5 and a 3.5 power valve and still get the same result. holley says this is ok as the carb is probably getting a signal from the engine to make this primary booster circuit go to work early. juts are right size and the floats are adjusted right and needle and seats are new.. new motor is going in and i just feel uncomfortable with this situation. new motor may have a whole different vacum reading(itsa a radical 377 cube in. sbc) coild anyone explain this whole situation to me and tell me if you think everything is normal. the car always ran great, just dont understand all that gas at high idle thANKS ART

  2. #2
    Senior Member SENIOR BUILDER
    Join Date
    Dec 2007
    Location
    Morrison, Colorado
    Posts
    120
    I'm no expert, but from what I've learned, you probably have the butterflies open too far, providing enough signal to start the mains flowing. Air bleed adjustments and other tuning changes may be needed on your combo to fix this. You should NOT have fuel flowing through the mains at idle at all. All the fuel should be supplied by the idle and transistion circuits. If the carb is tuned right, you'll have about .020" of transfer slot showing and the idle mixture screws out 1-2 turns or so.
    Mark Goulette
    Owner/Driver of the Livin' the Dream dragster
    www.livinthedreamracing.com
    Speed kills, but it's better than going slow!!!!

  3. #3
    Senior Member MASTER BUILDER
    Join Date
    Mar 2008
    Posts
    173

    holleys

    thanks colorado racer. the first carb is old and only has primary adjust needles(old metering blocks. the second carb with the new race center has air bleed jets that can be changed. what would i do with these jet type adjusters, go smaller or large, in the front or back, and in the front or rear. i really dont have a clue about these air bleeds setups. this carb also has the old metering blocks with NO adjustment screws in the blocks. thanks art

  4. #4
    Senior Member SENIOR BUILDER
    Join Date
    Dec 2007
    Location
    Morrison, Colorado
    Posts
    120
    Do you have a pin guage set or a set of numbered drill bits and a dial caliper? If so, you can gently insert the guages or bits into the air bleeds that are already there (there are some in there I'm assuming) and then measure to see what size they are. The outside ones will be for the idle circuit and the ones closest to the squirter nozzles will be for the mains. All of the outside ones should be the same size, and the inside ones should be the same size as well, but smaller than the outsides. What model of carb is this?
    Mark Goulette
    Owner/Driver of the Livin' the Dream dragster
    www.livinthedreamracing.com
    Speed kills, but it's better than going slow!!!!

  5. #5
    Senior Member MASTER BUILDER
    Join Date
    Mar 2008
    Posts
    173

    carb boosters

    thanks colorado. i will talk to my engine builder he did the first carb amd i did the second and they both do the same thing, so i think the reason is the engine. alot of head and intake port work with real low vacum and i just have to idle it high and am probsably opening the blades up front a whole lot.. my new motor is a high tech engine, but may give the carbs a different signal. what do you think. thanks art in NY

  6. #6
    Senior Member SENIOR BUILDER
    Join Date
    Dec 2007
    Location
    Morrison, Colorado
    Posts
    120
    Engine configuration can definately affect how the carb reacts on it. The big part is getting the carb tuned properly for the engine it's on. While there are countless racers out there that run out of the box carbs and do well, or use a buddy's carb and run well, it's also a well known fact that alot of the carbs out there are way out of calibration and can see substantial improvement when properly tuned to the engine they are being used on. Best of luck, let me know who things go!
    Mark Goulette
    Owner/Driver of the Livin' the Dream dragster
    www.livinthedreamracing.com
    Speed kills, but it's better than going slow!!!!

  7. #7
    Senior Member MASTER BUILDER
    Join Date
    Mar 2008
    Posts
    173

    boosters

    thanks colorado. one last question and to me important. while my engine is idling high and i am seeing the gas flow steadily from the front boosters is that a problem(maybe wash the cylinders out) or is that normal in the carbs function at this speed thanks art

  8. #8
    Senior Member SENIOR BUILDER
    Join Date
    Dec 2007
    Location
    Morrison, Colorado
    Posts
    120
    There are actually two answers to your question. The first is yes, it's normal for the mains to be coming in when there is sufficient throttle opening to allow for enough signal to begin drawing fuel from them. The second, it no, it's not normal for them to be working at idle! Even if your idle is a bit on the high side, you should not be pulling fuel from the mains! What this means is that you are having to open the throttle too much to achieve desired idle, and you're bypassing the idle circuit and transfer slots. This is something that needs to be corrected, and can cause alot of problems. Throttle response, cylinder washdown, diluted oil, and other things come to mine. If the carb is correctly calibrated for your combo, and everything is adjusted right, you should have about .020" of transfer slot showing on both primaries and secondaires (if this is a mechanical secondary carb that is), and the idle mixture screws should be out from about 1-2 turns. You should be able to achieve the correct idle speed with small adjustments to the mixture screws, not the throttle plates. It's also common for the throttle plates to have small holes drilled in them for the purpose of bypassing air to help with idle.

    Anyway, hopefully this will help you out some. Like I said, I'm no expert, and am still learning myself, but have gotten alot of information from people that know alot more than I do and I'm just trying to pass that info on to you. Let me know if I can help any more.
    Mark Goulette
    Owner/Driver of the Livin' the Dream dragster
    www.livinthedreamracing.com
    Speed kills, but it's better than going slow!!!!

  9. #9
    Senior Member RACING JUNKIE
    Join Date
    Mar 2006
    Location
    EUGENE,OR.
    Posts
    3,408
    I am not an expert either, but I have been through what colorado is saying & find it to be accurate. I ended up drilling holes in the primaries once on a 850DP BBC that had very low vacuum (4.5 inches) & a bigger cam... due to the same issue. Prior to that, had ring-wash & had to change the oil allot! The holes were about 1/8" specifically located inside mid primary area if I remember correctly. Ran a primary PV 3.5 & had to play around w/ a few sizes... finally got it all correct & the holes manipulated the x-fer slots being bypassed & dumping unnecessarily fuel @ idle.
    "I would walk through hell on Sunday before I fear the enemy"


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Email us - Support@RacingJunk.com
Call us - 866.326.9227
Copyright © 2005-2016 RacingJunk.com All Rights Reserved.

Designated trademarks and brands are the property of their respective owners. Use of this Web site constitutes acceptance of the RacingJunk.com
Terms of Use, Classifieds Disclaimer, Privacy Policy, and Cookie Policy