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Thread: Backfiring R100RT and Air Injector removal

  1. #1
    Vintage User nevada72's Avatar
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    Backfiring R100RT and Air Injector removal

    For posterity if nothing else -

    I've been resurrecting an 83 R100RT that "ran when parked". I wasn't looking, it just fell into my lap. In my process of getting the old gal going I've posted up a number of questions here, and the membership has been beyond helpful. The bike went from non runner, to hard starter/poor runner, to good starter/not so great runner. to so-so runner with some significant decel pop.

    That's what this thread is about. I got the bike to the point that it reliably started and was ridable. But it ran unusually hot, and there was some pretty annoying decel pop. Knowing something about bikes I hoped it was air being introduced into the exhaust somewhere. I further hoped that the 80s era EPA garbage was the culprit. So I forged ahead with the EPA kit from Bob"s BMW. There are plenty of examples on how to remove this troublesome plumbing so I won't go into that. What I will say id that removing it made far more difference than I ever imagined. It not only reduced the decel pop - it eliminated it. It also alleviated the hot running condition. I can honestly say removing the EPA stuff transformed the bike.

    Proviso - the hardware holding the plumbing to the head was finger tight. I suspect it was a huge air leak. Also, the vacuum hose between the carbs and the T at the air box was improperly removed, allowing unfiltered air into the box, which I remedied.

    Anyway, I am happy to say the bike runs out pretty darn well now. A carb balance will probably cure the last remaining issue - it's a little sluggish off of a stop.

    Again - thanks to all that helped!
    1971 R75/5 - 1983 R100RT

  2. #2
    Registered User lkchris's Avatar
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    An air leak at that point would be mostly meaningless other than perhaps the noise.

    Speaking of air leaks, on models with the pancake air filter it's good to check the condition of (and presence of) the airbox water drain valve. It's on the clean side of the filter, and if not sealing properly is a dirt ingress threat.

    When we had three Airheads, I ordered used parts from Motobins to obtain the Euro airbox lower part, which doesn't have the holes for the air ingestion system. Looks incrementally cooler than timing plugs.

    As regards the carbs, it may be useful to know Bing recommends replacing diaphragms something like yearly. In any event, they're probably toast on a "resurrected" bike.
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S, '84 R80G/S

  3. #3
    Vintage User nevada72's Avatar
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    Quote Originally Posted by lkchris View Post
    An air leak at that point would be mostly meaningless other than perhaps the noise.

    Speaking of air leaks, on models with the pancake air filter it's good to check the condition of (and presence of) the airbox water drain valve. It's on the clean side of the filter, and if not sealing properly is a dirt ingress threat.

    When we had three Airheads, I ordered used parts from Motobins to obtain the Euro airbox lower part, which doesn't have the holes for the air ingestion system. Looks incrementally cooler than timing plugs.

    As regards the carbs, it may be useful to know Bing recommends replacing diaphragms something like yearly. In any event, they're probably toast on a "resurrected" bike.
    Good points.

    On the air leak - I can say with a certainty that removing the EPA stuff and plugging the system eliminated the decel pop. I really didn't do much else that would account for such a profound difference. I used this as a reference - http://bmwmotorcycletech.info/pulseair.htm

    Water Drain valve - per the article above, I removed and plugged it.

    Bing diaphragms - correct. They were toast. I had the carbs rebuilt and all soft parts replaced.
    1971 R75/5 - 1983 R100RT

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