Idle Surge In Gear

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by BEDNAR1320, Mar 13, 2017.

  1. BEDNAR1320

    BEDNAR1320 Member

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    I've searched on here but thought I'd start a new thread to see what everyone's thoughts are for my situation.

    This is a BBC 12° head deal, 14-71 HH, setback rotors, four blade hat. It idles stable in natural, but as soon as I put it in gear it surges enough to make staging a challenge. I've tried curing this by adjusting the BV without any success. That being said I do have a fuel distribution issue at idle. Numbers 1-2 are very fat at idle and the rears are hot and lean, so I can't richen the BV any more without causing #2 to go out at idle, if I lean it the rear cylinders will be over 1000° at idle. Not sure if this is causing the surge or not. The throttle blades are at .012 and both stops are contacting solidly, so there is no twist of the shaft. At WOT the fuel distribution is not a problem, the plugs are very even front to rear with very little stagger in the port nozzles.

    I only have the blower at 13% OD, but it does make 27# and I don't really have the need or want to run more boost or OD.
     
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  2. HootersFunnyCar

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    What RPM are you trying to idle at?
    You can try opening up a hole after the blades to help from sucking them closed.
    .012 seems a little tight on the blades. What hat are you using?
     
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  3. BEDNAR1320

    BEDNAR1320 Member

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    It's a CF JBR four blade.
     
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  4. jay70cuda

    jay70cuda Member

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    I've had that happen when the valve cover blow off vents get plugged up too. I had a vent at the rear of the car in the puke tank get blocked. Once the slightest bit of meth got to the filter it suffocated the engine at idle.
     
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  5. LSR FC

    LSR FC New Member

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    Idle poppet pressure too close to pump pressure at idle opening and closing while in gear?
     
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  6. TADHemiracer

    TADHemiracer Member

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    Idle poppet pressure too low. I have mine at 8-11 pounds and the problem vanished.
     
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  7. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    I had a customer's car that wanted to do the same thing, surged no matter what I did with the BV, air, opening, bleeds, etc. They had a very strong return spring on it, all on the right side. we took that off and went to a normal return spring and it went away. It was flexing the shaft and the blades on that side, then it was cycling the spring, so it was constantly surging.

    That would be easy enough to check before you go dropping your idle check way down.

    If it isn't return spring or idle check, it could be the primary check needs to be raised, as it may be surging through the primary nozzles going to the intake.
     
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  8. BEDNAR1320

    BEDNAR1320 Member

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    My idle check is at 15#, port at 26#. I do have only one return spring on the right side, not a strong spring though. I'll check that, thanks Will.
     
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  9. Mike Canter

    Mike Canter Top Dragster

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    Change you idle check to 9-10 lbs. This will require a readjustment of the barrel valve leakdown. Normally on a hemi that 9-10 lbs requires about an 82-83% leakdown. If you are at 15 lbs now normally means you are at 77-80% leakdown. The two work together.
     
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  10. BEDNAR1320

    BEDNAR1320 Member

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    Mike, are you thinking that the idle check may be opening and closing once I put in gear and the pump speed slows down?
     
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  11. Mike Canter

    Mike Canter Top Dragster

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    Could be. What rpm does it idle at in gear and out of gear? What converter drive do you have
     
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  12. BEDNAR1320

    BEDNAR1320 Member

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    In gear it surges between 1600 and 2600. Out of gear 2200ish. This is a powerglide.
     
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    Last edited: Mar 13, 2017
  13. TADHemiracer

    TADHemiracer Member

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    Sounds to me that your hat nozzles are too big and that is only feeding fuel to the front two nozzles. How any hat nozzles and what nozzle sizes in your hat?
     
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  14. TADHemiracer

    TADHemiracer Member

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    Try putting a 30# poppet in the front two nozzles putting the fuel further back in the hat.
     
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  15. Randy G.

    Randy G. Top Alcohol

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    rich....lean....rich....lean....rich....lean....
     
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  16. Bjs344

    Bjs344 Member

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    Have you checked your poppets since the problem started? Every time mine starts surging I find that the idle poppet isn't seating fully. Clean it up and it immediately idles better.
     
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  17. BEDNAR1320

    BEDNAR1320 Member

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    I haven't, but I will....
     
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  18. td3829mk

    td3829mk Member

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    What's the "optimal" opening with a 4 blade hat? I have always seen/heard .012 is right around where it should be set
     
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  19. Mike Canter

    Mike Canter Top Dragster

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    I think .012" is right on for a 4 bladed hat with a converter. You are trying to get the idle rpm down to a stable 1800 and with a bigger gap than that it just ain't going to happen.
     
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  20. BEDNAR1320

    BEDNAR1320 Member

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    Thanks Mike!
     
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