Backfire.....Intake Leak?

Discussion in 'Engine, Fuel and Exhaust' started by propflux01, Jan 19, 2014.

  1. propflux01

    propflux01 Active Member

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    Wife's '03 RK started to develop a decel backfire. Loud pop out the pipes. Rode behind it, and when it backfired I could see the 'fire' come out of the left side. I also have been noticing, when starting cold, the idle will slowly vary from 1000 to about 1150, and back to 1000 in about 10 second intervals. Just a wavering up and down idle. Goes away and idles normal to slow when warm. So last week I completely removed left side (true duals, Rineharts) and installed a new port gasket, and new TORCA clamp, and Copper RTV'd the heck out of the slip joint. let it dry for two days before starting it. Rode 200 miles today, and the pop is back. I can no longer see the 'fire' pop out the back of either pipe, but I sure can hear it. It is a random loud backfire, only on decel.

    Bike is 95 CI, 94K miles
    Unknown Cam ( But almost sure it is an SE Cam, as previous owner stated HD dealer did the Gear drive and 95 update at 20K)
    PC lll (never had issues, and never been tampered with since install)

    Now, my question is, since I have resealed the exhaust (again) and when putting my hand over the pipe I cannot feel any leaks, could an intake leak be causing this? I tried spraying brake cleaner on the manifold but couldn't tell any change.
     
  2. tourbox

    tourbox Senior Member

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    I've never tried Brake Cleaner. I don't know if it is combustible or not. Probably so. I usually use Carb. cleaner or WD40. I know they will give you an RPM change. Other people use propane gas to do it with(unLit), I just don't have a propane torch.
    tourbox
     
  3. propflux01

    propflux01 Active Member

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    I usually use brake cleaner because it doesn't burn as well as carb cleaner and usually RPM will go down. Or maybe I am wrong in my thinking? Just trying to figure if maybe old intake seals would cause this since I've been through the exhaust.
     
  4. tourbox

    tourbox Senior Member

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    Well I guess Brake cleaner will work then. You said you didn't notice any RPM changes when sprayed. An intake leak could be sealing better when warmed up than cold motor. Was the motor warmed up or cold when checked for the leak at manifold.Leaking manifold can cause the idle RPM to fluctuate. Do you know how long the existing manifold gaskets have been on there,years versus mileage? If it's been several years or a lot of miles you may need or want to change them for peace of mind. Another thing you could try is removing the PC111 and try that.
    tourbox
     
  5. Harttoo

    Harttoo Senior Member

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    I had a rear cylinder intake leak last summer on 2012 Limited.Ran fine till warmed up then ,intermittent missing around 2000 rpm.Dealer found by squirting light oil near intake,killed engine.
    My bike never backfired,but it ran hot because rear cylinder was so lean.Sucking air and missing.
     
  6. propflux01

    propflux01 Active Member

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    I was figuring maybe the backfire was possibly related to the wavering cold idle. When I checked with the brake cleaner it was started for about 5-10 minutes
     
  7. lakevillehog

    lakevillehog New Member

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    I am no pro mechanic but I have had the same issue and mine was caused from the exaust clamp being loose and drawing O2 in
    simple fix if that is it
    also check for holes in exauste
     
  8. HDDon

    HDDon Experienced Member Contributor Retired Moderators

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    After you're sure there are no leaks try cleaning the IAC. Check the self help for all the info you need.