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Thread: 03' RT Light Backfire at 62k miles

  1. #1
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    03' RT Light Backfire at 62k miles

    Bike developed an occasional light backfire on deceleration/drop throttle after an extensive “tune-up” last spring at 62k miles. Other than backfire, bike runs well: starts quickly, smooth idle (which is a little low), linear throttle response, no surging, with good gas mileage (45mpg). I have two questions: Is the backfire a concern? And if it is, any suggestions to eliminate it? Maybe caused by a leak in TB intake?
    More info on the bike: tune-up included professional injector cleaning, cleaning of TB and BBS ports, removal/cleaning of the Bowden cable box (a real PIA.) and throttle body sync per roger 04 rt instructions. TPS reads 250mv at idle position. Installation of Autolite 3923 plugs @0.25” gap in June did not affect backfire. Valves were last adjusted at 55k miles on 9/16.
    Ken S
    03 R1150RT

  2. #2
    Left Coast Rider
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    My WAG would be to back out each BBS 1/8 turn and see what happens. More educated minds will likely prevail...

    PS I think your bike is not backfiring, I think you have a lean idle setting which doesn't allow complete combustion thereby allowing unburned fuel to collect in the exhaust system and then "pop" when hot gases ignite that fuel.

  3. #3
    Pepperfool GSAddict's Avatar
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    Before chasing anything in the intake system make sure there are no air leaks in the exhaust system. Check where the header meets the muffler assy. I solved a popping issue on an 1150RT 2 years ago with high temperature silicone and reassembling that joint. Also check the head to pipe joints.
    '
    Ufda happens..........

    Need your R11xx Hall sensor rewired? PM me.

  4. #4
    Registered User rogerc60's Avatar
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    My '03 R1150RT has done this since I bought it a little over a year ago. Being the first BMW I've ever owned, and the first motorcycle I've owned in 30 years, I thought it was normal.

    How does one go about testing for exhaust leaks in those spots?

  5. #5
    Registered User m_stock10506's Avatar
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    Quote Originally Posted by BC1100S View Post
    My WAG would be to back out each BBS 1/8 turn and see what happens. More educated minds will likely prevail...

    PS I think your bike is not backfiring, I think you have a lean idle setting which doesn't allow complete combustion thereby allowing unburned fuel to collect in the exhaust system and then "pop" when hot gases ignite that fuel.
    BC1100S, why back out the BBS? Doesn't backing out the BBS make the idle leaner?

    "Light" popping when you shut down the throttle and allow the engine to slow the bike is normal.
    Michael Stock, Trinity, NC
    R1100RT, R100, R60/6

  6. #6
    Pepperfool GSAddict's Avatar
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    Quote Originally Posted by rogerc60 View Post
    My '03 R1150RT has done this since I bought it a little over a year ago. Being the first BMW I've ever owned, and the first motorcycle I've owned in 30 years, I thought it was normal.

    How does one go about testing for exhaust leaks in those spots?
    A dead giveaway is black soot at the fitting/junction.
    '
    Ufda happens..........

    Need your R11xx Hall sensor rewired? PM me.

  7. #7
    Pepperfool GSAddict's Avatar
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    Quote Originally Posted by nosvamos View Post
    Bike developed an occasional light backfire on deceleration/drop throttle after an extensive “tune-up” last spring at 62k miles. Other than backfire, bike runs well: starts quickly, smooth idle (which is a little low), linear throttle response, no surging, with good gas mileage (45mpg). I have two questions: Is the backfire a concern? And if it is, any suggestions to eliminate it? Maybe caused by a leak in TB intake?
    More info on the bike: tune-up included professional injector cleaning, cleaning of TB and BBS ports, removal/cleaning of the Bowden cable box (a real PIA.) and throttle body sync per roger 04 rt instructions. TPS reads 250mv at idle position. Installation of Autolite 3923 plugs @0.25” gap in June did not affect backfire. Valves were last adjusted at 55k miles on 9/16.
    Note: a better plug for the 1150 is the 3922 (1 step cooler)
    The 3923 is typically used on the 1100's
    Stock gap @.032"
    '
    Ufda happens..........

    Need your R11xx Hall sensor rewired? PM me.

  8. #8
    Left Coast Rider
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    Quote Originally Posted by m_stock10506 View Post
    BC1100S, why back out the BBS? Doesn't backing out the BBS make the idle leaner?
    Y'know, I wasn't totally sure which way to turn the screws on that point which is why I noted it with a WAG (wild assed guess). Thanks for catching that. I was also fairly sure that GSAddict would chime in to clean up any mess I made.

    I never experienced any audible popping on my S but I had an AX-FIED installed. I also typically travel faster than the speed of sound.

  9. #9
    Quote Originally Posted by GSAddict View Post
    Note: a better plug for the 1150 is the 3922 (1 step cooler)
    The 3923 is typically used on the 1100's
    Stock gap @.032"
    Pull the plugs and check the gap. I had a bike that did this after I change the plugs. To stubborn to check and when I did one was almost 5 thousands to tight regap and the backfiring went away.
    1999 Triumph Tiger, 1998 K1200RS, & 1994 R1100RS

  10. #10
    Registered User ALIENHITCHHIKER's Avatar
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    Okay - I know this is thread drift - but I just have to ask while the thought is fresh in my head - what is the performance effect of slightly widening the plug gap, pushing it out to .035 or or so ?
    Steve
    Current Hottie: '00 R1100RT
    Old Flames: '85 K100RT, '80 Yamaha XS850, '67 Triumph Bonnie, '66 Honda 90 Scrambler

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