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Boxer stumble

Discussion in 'Technical Q&A' started by boxerman, Oct 2, 2006.

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  1. boxerman

    boxerman F1 World Champ
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    Sean
    #1 boxerman, Oct 2, 2006
    After changing the exhaust on my boxer the car developed an intermittent of idle stumble. For example when pulling away from a stop the motor would go flat like it stalled, but did not. This did not happen every time. Lately this problem is all the time, car also stumbles below 3500 rpm, seems to buck and kick whle pulling off, above 400rpm it clears and is as strong as ever. Seems fine on the highway from 3000 rpm on. Lastly when pulling off it now needs more revs and reving at standstill can give an exhaust pop,like unburned fuel. Basicaly car seems to drive like an old carburator v8 that is not warm with the choke on. Any ideas?
     
  2. J.P.Sarti

    J.P.Sarti Guest

    May 23, 2005
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    #2 J.P.Sarti, Oct 2, 2006
    check your wires on the cap, could have been bumped, remove the cap look for signs of corrosion from misfire as well, check other connections such as coil and ign box, sounds ign related
     
  3. GCalo

    GCalo F1 Veteran

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    Greg Calo
    #3 GCalo, Oct 2, 2006
    While I have no experience with the Boxer, most free flow exhausts function to limit back pressure (internal muffler pressure) and to allow a better flow of exhaust gasses.

    If it's not an electrical problem as a result of bumping something during the installation, It seems that your new exhaust may be drawing more fuel through the system due to the lower restriction and is affecting the mixture.

    Maybe you need F/A ratio adjustments.
     
  4. Ken

    Ken F1 World Champ

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    #4 Ken, Oct 2, 2006
    Absolutely. You go way lean when you change to a freeflow exhaust. Check a few spark plugs and see if they're white. You may need to rejet your carbs if it's a carb car. Either way, you need a tune up!

    Ken
     
  5. boxerman

    boxerman F1 World Champ
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    #5 boxerman, Oct 2, 2006
    Mixture was adjusted. Backfire in the exhaust seems to indicate unburned fuel. Car is injected, exhaust may just enhance prexisting problem.
     
  6. GCalo

    GCalo F1 Veteran

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    #6 GCalo, Oct 2, 2006
    That's the point I was getting at. I think there is too much fuel.

    So, pull a plug and look at it. The color will tell you a great deal.

    Could be also your FI system is pumping too much fuel.

    Whatever it is, your new muffler is not "causing" the condition. It is merely bringing the issue more to light.
     
  7. JTR

    JTR Formula 3
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    #7 JTR, Oct 2, 2006
    I’ll echo Sarti on this one.
    Pull the distributor cap. My BB had similar symptoms and the inside of the cap had a bunch of green ‘growth’ around the contacts, and on the rotor contacts. A good clean-up cured the problem.
    PS. Also be sure the center carbon piece in the center of the cap is free to slide in and out. Mine was sort of stuckish.
    John
     

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