Loads up at idle

Discussion in 'Holley' started by Tony, Jul 17, 2007.

  1. Tony

    Tony Well-Known Member

    I have a Holley 950HP carb on top of my 455. It is a race only motor. When I sit in the lanes getting ready to make a pass the carb loads up BAD! I have my idle screws out 3/4 of a turn and there is no power valve in the back and I have a 4.5 power valve in the front. If I keep clearing the motor out before I make a pass then I'm okay, but if I have to wait on the other guy in the other lane then it loads up and stumbles when I go to accelerate. Would switcing back to a 6.5 power valve help or would going to a 3.5 power valve work better? HELP PLEASE,
    Tony
     
  2. Jeff Kitchen

    Jeff Kitchen Well-Known Member

    Try a 3.5 PV first. If that doesn't do it you may need to enlarge the idle air bleeds a little. While you have it off, check your throttle blade positions. None of them should be higher than the middle of the transfer slot at idle. If you have the front open too far, close them back down and open up the rear to compensate. When the carb is right, all four throttle blades should be uncovering about 0.030" of the transfer slots at idle. You may be pulling fuel from the main circuit now, causing an over-rich condition.

    Have fun.
     
  3. Tony

    Tony Well-Known Member

    Jeff, thanks for your reply. If I change the idle air bleeds do I have to change all four or just the front two? Will switching to a 3.5 PV hurt my down track performance or is a PV just for idle? I checked my vacuum at idle with a vacuum guage and it is at bounces between 7 & 8. Does the main jetting have anything to do with idle or are they just for off idle acceleration? When you speak of the ""transfer slot" what exactly are you talking about? I don't know much about carbs that is the reason for so many questions. This is the first problem that I have had with this carb since I bought it 5 years ago.
    Thanks once again,
    Tony
     
  4. telriv

    telriv Founders Club Member

    I'll add my .02c to this. Check your float levels 1st!!!!! Also floats DO go bad!!!!
     
  5. nailheadina67

    nailheadina67 Official Nailheader

    I also have 2 cents add here......keep in mind I'm not too good with Hollies......but once I had a 600 w/ vac secondaries that did the same thing, new out of the box, and the only cure was to use heavier springs under the floats. Tech support was useless.....that was my idea. I drove the car for 6 years like that and the flooding problem never re-appeared. :idea2:
     
  6. sailbrd

    sailbrd Well-Known Member

    +1
     
  7. Tony

    Tony Well-Known Member

    Thanks for everyones input. I did check the float levels and they are fine. I guess I should clearify something about how bad it loads up. My car will be fine as long as I do not have to wait on the guy in the other lane. This problem drastically affects my reaction time. I'll go from .010 lights to .130 lights because of a small stutter on the starting line due to the carb loading up. As long as I don't get in a staging duel, I'm fine. This problem does not hurt the cars et. It will run 11.44 to 11.46 all night long. Its the small stutter on the starting line that has been putting me on the trailer:af: :af:
    Thanks again,
    Tony
     
  8. sailbrd

    sailbrd Well-Known Member

    If your tuned correctly at idle with a 950 hp the vacuum should be rock steady. One of the nice things about them.

    Before you take off the carb to go to the next step check to see if your AP squirter's are leaking. On mine the adjustment was a little tight and made them drip a bit.

    The transfer circuits are the tiny vertical slots near the back of the throttle blades. By back I mean the half of the blade that will rotate down as you open the throttle. Jeff is right on the money here. Set the carb up with the .030 setting on both. On mine I set the idle screws at 1 1/2 turn out, this probably varies with motor.

    Start motor, will probably have high idle. Carefully tune idle with both screws, make equal turns only 1/8 turn at a time. Then go to the fuel adjustment screws. Nice to have an O2 meter here but can still do it the old fashioned way. At 1 1/2 turns out you are probably rich. Turn each screw in 1/8 until idle goes up or vacuum falls off. If idle goes up (it should) readjust then go back to fuel screws. If you end up bottoming out some of the idle mixture screw I think this would indicate a need for bigger bleeds. Did not have to do that with mine so have no experience there.

    Still learning about the 950HP but this worked for me.
     
  9. Jeff Kitchen

    Jeff Kitchen Well-Known Member

    The above post is right on, thanks. The number on the PV is the vacuum reading where it opens. You don't want it opening anywhere near idle. If you idle at 7-8, you might be getting into a 4.5 PV in gear. Try the 3.5 and see if anything changes. Once they are open, they all flow about the same amount of fuel.

    The air bleeds should be a last resort. Try the other things first, ONE THING AT A TIME. Find out what works and then you'll know what to do next time it acts up.

    Have fun.
     

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