Hunting while idling

Discussion in 'PSI Superchargers Tech Questions' started by Wildcatracing, Dec 17, 2009.

  1. Wildcatracing

    Wildcatracing Member

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    Hi there, this is my first post in this forum, all the way from New Zealand. I have a blown alcohol 509 BB Chev, enderle hat, port injection, 35% over 10-71, waterman 18.6 gpm pump, dart 360 heads, 25 deg timing trans brake Turbo 400 trans with convertor. The engine hunts terribly when in gear and I would appreciate some help regarding if it is lean or rich. The butterflys have approx .009 clearance and the BV was set at approx 70% leak. Cheers Graham
     
    #1
    Wildcatracing, Dec 17, 2009
  2. Wildcatracing

    Wildcatracing Member

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    Sorry, forgot to mention that the idle EGT's are around 500 deg F which implies its lean....
     
    #2
    Wildcatracing, Dec 17, 2009
  3. Mike Canter

    Mike Canter Top Dragster
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    So what is the idle return poppet set at and what RPM are you idling at. I think your leak down on the BV may be a little off. Hunting like that can because of several things but normally because the idle return poppet is opening and closing. I usually set the gap on the butterflys .012, the idle poppet at 8-9 lbs crack pressure and the BV leakdown at 78-83% with the idle return blocked and the line out disconnected on the BV. Normal idle RPM is 1800 to 2000 but that maybe hard with a converter.
     
    #3
    Mike Canter, Dec 17, 2009
  4. ITS IN MY BLOOD

    ITS IN MY BLOOD TAFC

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    What does the rpm drop to when put into gear,..
    idle rpm,..???
    in gear rpm,..????

    500 aint nothing ??? you could be retarded a couple of degrees in timing from what the motor wants, and so the flame is burning in the pipes at the egt..
     
    #4
    ITS IN MY BLOOD, Dec 17, 2009
  5. Wildcatracing

    Wildcatracing Member

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    thanks guys, the idle poppet is only 3-4psi, the idling appears to be from 700-1900 rpm
     
    #5
    Wildcatracing, Dec 17, 2009
  6. vwsamba

    vwsamba Member

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    mine did exactly the same thing on first fire up. it turned out to be way too rich. 5 flats on the barrel valve(left is lean) cured it and it idled smooth around 2000 rpm after that. good luck.....
     
    #6
    vwsamba, Dec 17, 2009
  7. Mike Canter

    Mike Canter Top Dragster
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    Set that idle poppet to around 8 lbs crack and it will probably smooth out. Once it does then you may want to play with the leakdowm. I doubt that 70%is too rich but it might need to be adjusted to 75 or 80%.
     
    #7
    Mike Canter, Dec 17, 2009
  8. jim phillips

    jim phillips ta/fc

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    what BIG MIKE said sounds good it can be adjusted out
     
    #8
    jim phillips, Dec 17, 2009
  9. Wildcatracing

    Wildcatracing Member

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    thanks again for your help guys, I will let you know how I go. Have a great Xmas !
     
    #9
    Wildcatracing, Dec 17, 2009
  10. Mike Canter

    Mike Canter Top Dragster
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    Let me add an expanation on the primary cause of idle hunting as I have been taught (anybody correct me if I am wrong). As we know the pump pressure changes with motor RPM. If the poppet is at the wrong crack pressure say like at 3-4 lbs (which is too low)and you try and bring the motor RPM at idle to 1900 RPM then the pump pressure increases and the idle poppet opens and dumps fuel back to the tank and the motor goes a little leaner and the rpm drops and the poppet closes again. Now the idle gets richer and the motor speeds up again and the poppet opens again and the motor slows down again and on and on. This makes the motor hunt for the right RPM. So if you bring the idle poppet up to 8-9 lbs crack pressure now the poppet will most likely stay closed during idle so the idle mixture can be controlled just by the BV mixture adjustment and the idle mechanical screw adjustment and the RPM should stay more constant.
     
    #10
    Mike Canter, Dec 17, 2009
  11. ITS IN MY BLOOD

    ITS IN MY BLOOD TAFC

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    uH,...Mike...Doesnt the motor rpm go up if you lean it...:rolleyes:

    Just checkin,....:D
     
    #11
    ITS IN MY BLOOD, Dec 17, 2009
  12. Mike Canter

    Mike Canter Top Dragster
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    Correct, but that is with a massive lean out. We are not talking about that kind of lean out.
     
    #12
    Mike Canter, Dec 18, 2009
  13. Dave Koehler

    Dave Koehler Member

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    Better add in butterfly stop adjustment here also.
    IF you adjust the BF/BV reset the stop on the other side. IF you don't the BFs will flex and aggravate the "hunt". It's worse with blowers.

    Dave Koehler
    http://www.koehlerinjection.com
     
    #13
    Dave Koehler, Dec 18, 2009
  14. Mike Canter

    Mike Canter Top Dragster
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    You are correct and that is what I meant by idle mechanical screw adjustment. Your definition is better and clearer than mine.
     
    #14
    Mike Canter, Dec 18, 2009
  15. fasttimesracing

    fasttimesracing Member

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    my motor will do the same thing with the timing low like that also.
     
    #15
    fasttimesracing, Dec 18, 2009
  16. Ken Sitko

    Ken Sitko Super Comp

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    Back when everyone used to run their idle checks at 3 psi, I had a pretty bad experience that made me switch to the 8 to 9 lbs that Mike is talking about. Every time I did a burnout with our TAD, which seemed to be running fine, by the time I staged the car, their were no pistons left in it. Send the fuel system to Walt at the time, and it turns out the bv was leaking, and being at such a low pressure, it roasted all the pistons. Put a new bv in at 8 lbs, and the problem was gone.
     
    #16
    Ken Sitko, Dec 18, 2009
  17. Wildcatracing

    Wildcatracing Member

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    Hi everyone, happy new year to you all. W went racing with no changes other than the 8lb sec bypass and the hunting was basically the same. Upped timing from 25 to 29 deg and bugger all difference. Increased the butterfly clearances slightly and the hunting has improved heaps. Its still idling a bit high for my convertor (1800rpm) but it is manageable. Sadly I blew the sprag in 2nd on my T400 just as the engine was coming right !! Cheers Graham:)
     
    #17
    Wildcatracing, Jan 5, 2010
  18. 560Jim

    560Jim Member

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    Hunting

    Hi GC,
    Ive sent you a PM
    Jim
     
    #18
    560Jim, Jan 5, 2010

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