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1Back to top Go down   89 K100rs occasional backfire when hot Empty 89 K100rs occasional backfire when hot on Fri May 24, 2013 12:15 pm

thal13

thal13
active member
active member
My recently acquired and rehabilitated k100rs has been running pretty well, but I really have no basis of comparison since this is my first experience with any K bike, so it might be that it could run even better with some additional TLC.

Since I replaced the fuel pump and got it running, it 'burbles' and occasionally backfires but only during light engine braking with a partially opened throttle. The burble actually sounds good to me, but if it's not supposed to do that then I need to rectify it. I read that the FI will cut delivery above 2000 rpm if I chop the throttle completely, but if I'm using slight engine braking with minor throttle then fuel is still being injected...right?

So what should I know? It has an aftermarket Staintune exhaust, so it might be a backpressure thing that's pretty normal, or is it likely a timing issue? I don't seem to have any flat spots in power delivery, and the bike runs incredibly well at both low speeds and prolonged highway runs. I've ridden other "modern" FI bikes with terrible snatchy on/off throttle characteristics, and I can't believe that BMW got it so right so early. Thanks for any thoughts,

thal13

    

MikeP

MikeP
Life time member
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Is the Staintune a complete system or does the silencer clamp to the header pipes?

I ask because K75 models that have a separate silencer are prone to backfires if the seal between the pipes and the silencer is drawing in cold air, cured by sealing the join properly.

Same thing occurs with R1150 models that have a similar system.

    

charlie99

charlie99
VIP
VIP
fairly common issue

i found after sealing up the inlet path (those rubber adaptors etc around the throttle bodies and head flanges ) that the old stayintune has far less burbles and backfires these days

it does have a different note to the standard muffler systems though ...

if you have a collector type system i would do as mike suggests

hope that helps


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'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O89 K100rs occasional backfire when hot Au-log10

'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
    

thal13

thal13
active member
active member
Thank you mike and charlie. I'll have to take a close look at the exhaust and header connections. Like I said, the burble doesn't bother me at all, in fact it reminds me of my old '66 Fury II hobby car- that V8 made a similar burble & it had the power to back up all that muttering and complaining at low speeds. Just don't want any actual explosions that aren't whacking a piston at the right time.

    

5Back to top Go down   89 K100rs occasional backfire when hot Empty I have an 85rs on Fri May 24, 2013 7:32 pm

ibjman

ibjman
Life time member
Life time member
I have an 85rs and it has the throttle position switch on the end of the throttle body shaft. Fuel cutoff on de-celleration has to have two conditions to activate. It must be above 1500rpm (maybe 2000?) AND the throttle must be completely closes. As soon as the TPS see's any application of throttle, it switches fuel back on.
This is all if the TPS is correctly adjusted, so that it switches "off" just a hair above the closed throttle stop.
Mine backfires into the silencer very rarely..........this occurs when using engine braking as you describe and just at the moment the fuel switches back on.
This doesn't match your symptom exactly, but it may provide some background info.
Properly adjusted if you listen VERY carefully you should hear the switch click on & off when moving the throttle linkage off its base stop by hand. Many people adjust it with an ohm meter.
Also many imtentionally adjust it so that it never quite activates at closed throttle to avoid the cut off entirely. They say it reduces the lurch & snatch plus gives quicker power response in the twisties.
For me, I keep it adjusted as designed.

    

6Back to top Go down   89 K100rs occasional backfire when hot Empty Re: 89 K100rs occasional backfire when hot on Fri May 24, 2013 11:22 pm

thal13

thal13
active member
active member
Good info ibjman- thank you. I'm very happy with throttle response currently, and while I haven't heard the fuel switch on/off, I can definitely sense it at times when engine braking. It's never abrupt, just scarcely discernible.

    

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