Decel popping

Discussion in 'Engine, Fuel and Exhaust' started by glider, Jul 2, 2011.

  1. glider

    glider Veteran Member

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    Popping is basically caused by a leak in the exhaust system possibly at the head pipe or at a joint in the system that draws in air. When any unburnt fuel exits the cylinder like on decel, the air that can leak into the system will cause the mixture in the system to ignite causing a pop. Check your system for leaks and repair as necessary.

    To locate any leaks you may have at the joints in the exhaust or at the mufflers, try starting the bike and with some heavy gloves on, block the exhaust at the outlets and listen for a hissing. You can locate any leaks this way.
    It may be better if you have a helper listen for the hissing while you block the exit of the exhaust from the mufflers.
     
  2. Dark Ker

    Dark Ker Member

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    In answer to your Rich Vs. Lean question; It can be either. In my experience, most of the popping is from a leak as the previous poster said.
     
  3. dieselguy65

    dieselguy65 Account Removed

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    popping is caused by a leak in the system, or a lean condition. Tuned lots of carbs, on every kind of engine around and never had a rich mix make it pop on decel. check exhaust, a very small leak that you cannot hear or easily notice will draw air in on decel. if nothing there, rich up the idle just a touch
     
  4. glider

    glider Veteran Member

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    To properly set the mixture, the idle mixture screw has to be uncapped and adjusted.
     
  5. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    Doesn't sound like he knew what he was doing. Rejetting is going to necessitate adjusting the idle-air mixture needle to make sure the low speed is the right size. If adjusting the idle needle after replacing the low speed has no effect, the low speed is the wrong size. Don't know how he would have been able to just change the jets and NOT adjust the idle needle for optimum low speed performance.

    TQ
     
  6. glider

    glider Veteran Member

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    I agree with TQ. This mechanic either doesn't know the proper way of doing it or was just rushing and gave you an excuse. Unless you open up the idle mixture and adjust it properly, the low speed mixture where you do most of your riding will not be right.

    By virtue of what he told you, I would be reserved about using him.
    He should be able to remove the plug over the idle mixture and adjust it without any problems. If you go back to him, ask him how far open the idle mixture is when he's done. It should fall in the range of 2 1/2 to 3 turns open and if it doesn't then you have the wrong low speed jet in there.

    Sloppy work and bad practices IMO.
     
  7. glider

    glider Veteran Member

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    I've done it on the bike but it's close to do. You can turn the carb in the mount and get to it better or just pop it out of the compliance fitting.

    Read the tip in self help about jetting for more info.

    You have to be careful drilling it not to go through with any force and contact the screw itself or you can damage it.
     
  8. glider

    glider Veteran Member

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    The raising of the RPM is proof that it was lean to begin with and needed the additional fuel.

    Set idle speed to proper r.p.m. by adjusting the IDLE SPEED SCREW. Turn the IDLE MIXTURE SCREW open (after lightly bottoming it out) to achieve the highest steady speed and best response usually found at 2 1/2 to 3 turns open and fully warmed up. After adjustment has been made reset the IDLE SPEED SCREW to the proper r.p.m.

    Just opening it up to 3 turns open is better but still not right.
     
  9. glider

    glider Veteran Member

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    It may respond differently during a road test. The popping can be a result of after market mufflers which is usually the case with lower restriction. Stock mufflers will pop too but you don't hear it. If you were following someone, watch inside their muffler on decel and you will see a blue flame at times. That's what you are hearing from yours in the form of a popping.

    Exhaust leaks are usually the cause of excess popping.
     
  10. glider

    glider Veteran Member

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    An occasional pop on decel isn't anything to be concerned about. Best to find the leak if you can and do what's necessary to repair it.

    As far as the filter being on when you adjust it, as long as it's fairly clean there shouldn't be a problem.

    Harley Davidson Community
     
    Last edited: Jul 3, 2011