BMW K bikes (Bricks)

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1Back to top Go down    Engine popping on Sat 6 Sep 2014 - 18:40

BarryM

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My K1100LT makes some pretty good popping noises when I ride it so I thought I probably had some perished rubber around the air box or the injectors but now I've cleaned everything up I don't see anything obvious and the rubber still seems to be in pretty good shape for such an old bike. Are there any common causes of this sort of thing or shall I just ignore it, not the end of the world but I do leave the house early and although it doesn't happen on start up (it happens as I ride along) it would be nice if there was an 'easy' cure,

TIA

    

2Back to top Go down    Re: Engine popping on Sat 6 Sep 2014 - 18:50

Ghost who rides

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My immediate thought was "is it backfiring?" On my bike it was and I had to adjust the TPS (throttle position switch)

I see though that your bike is the 1100 which is Motronic, I think, which has a different TPS so this probably doesn't apply.

Is your Popping a backfire? Some Guru will chime in (within half an hour is my guess) with the answer.


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1986 †K 75 C † 2nd owner 187,000kms showing .
1987 †K100RT †Police repainted, rough and unloved.
    

3Back to top Go down    Re: Engine popping on Sat 6 Sep 2014 - 19:31

RicK G

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The most common cause is a leaking exhaust gasket letting some fresh air into the exhaust system.
You get hot carbon monoxide and some fresh air onto it and pop it burns and out comes carbon dioxide and noise.


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If everything seems under control then you aint goin fast enough:- Mario Andretti
Bikes 1986 K100RT, 1993 K1100 LT, 1994 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 & 1976 SR 500 Yamaha for now
    

4Back to top Go down    Re: Engine popping on Sat 6 Sep 2014 - 19:52

BarryM

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Thanks guys, I guess I need to decide if it's popping or backfiring, once it's back on the road in a week's time I'll work it out and follow up.

    

5Back to top Go down    Re: Engine popping on Sat 6 Sep 2014 - 21:40

charlie99

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possible a cracked exhaust ...where it joins the muffler ?† seems pretty common on 16 valve machines
but best money is on some form of leak on the intake rubbers ...
just my contribution


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'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
    

6Back to top Go down    Re: Engine popping on Sat 6 Sep 2014 - 22:01

mike d


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possible a cracked exhaust ...where it joins the muffler ? seems pretty common on 16 valve machines.

That's what caused the backfire on my K1100.

Mike

    

7Back to top Go down    Re: Engine popping on Sun 7 Sep 2014 - 0:25

robmack

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Backfiring is common on the K75 when the exhaust gasket that goes between the header and muffler deteriorates and allows air into the system, or when the head gaskets leak. †A leaking exhaust on the K100 would produce the same effect. †Popping on deceleration is usually a sign of lean fuel mixture but I've never heard of that condition happening on a classic K-bike. †It's more prevalent on modern bikes that are tuned lean to pass emission standards.


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8Back to top Go down    Re: Engine popping on Sun 7 Sep 2014 - 17:45

BarryM

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Thanks for the suggestions, my money was on the intake rubbers but those damned single use hose clips have meant I wonít be taking them off right now. I think Iíll finish off the work Iím doing now and once the bike is back on the road work out when itís popping and then look at your comments again.

    

9Back to top Go down    Re: Engine popping on Sun 7 Sep 2014 - 18:01

charlie99

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you can sometimes widen them with a set of circlip expanding pliers (the right angle ones )

it may help


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cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%O
    

10Back to top Go down    Re: Engine popping on Mon 8 Sep 2014 - 13:27

Be made

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BarryM wrote:Are there any common causes of this sort of thing or shall I just ignore it,
My 2 cents, right or wrong says:

1/ Don't ignore it. The bike needs to be sorted

2/ I had the same thing. So I Resealed where the 4 headers go in to the muffler. That didn't work. Further investgation with a torch up the muffler showed the baffle end plate had burst. a lot of popping, farting and banging went on with the bike and it seemed a little louder than normal. If it was me I would inspect the muffler baffle and if it lloks ok then remove† the muffler, give it a good rev just on the header pipes and see if it pops on decell. It shouldnt do that and if it doesnt then the muffler will be the culprit. If it does then it will be an air leak somehwhere else

    

11Back to top Go down    Re: Engine popping on Tue 9 Sep 2014 - 14:39

Holister

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Agree. Sort it out.

From what I can gather a little popping now and then is normal but back firing can damage the valves and could even be a symptom of damaged valves (prob unlikely tho in a K).

Mine would occassionally let out a loud crack like a gun shot usually when revs got down to the lower end.

I replaced the crankcase vent tube and exhaust gaskets. Number 2 had evidence of blow past.
After you've replaced them, nip the flange bolts up again after you've ridden it for a few days. Go for a fang... get the engine hot. You could try nipping up the flange bolts first to see what happens but the gaskets are cheap, easy to replace and they're probably due anyway.

Back firing is gone but I still get a little pop occassionaly.

Cheers


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1988 K100RT†††† VIN No.† 0094680
1989 K100RT † † VIN No.† 0097367 (naked)††
1996 K1100RS ††VIN No. †0451808
† † Fuel:† 95 Octane
Engine Oil:†Nulon Full Synthetic 15W50
Gear Box Oil:† Nulon Synthetic 75W90
    

12Back to top Go down    Re: Engine popping on Wed 17 Sep 2014 - 3:56

BarryM

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OK, so the bike's back on the road. The popping noise happens on a steady throttle as I ride along and although it's not particularly loud it is a bit irritating. It's definitely not a backfire so any suggestions on the cause as it's not really covered in any of the earlier posts!

    

13Back to top Go down    Re: Engine popping on Wed 17 Sep 2014 - 4:26

Avenger GT

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Are your exhaust valve clearances all right?

    

14Back to top Go down    Re: Engine popping on Wed 17 Sep 2014 - 8:00

BarryM

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Well they've not been checked for a few years so I couldn't say for sure, the bike doesn't do more than a few thousand miles each year so my maintenance schedule isn't quite as thorough as it might be Embarassed

I'm still thinking it could be an air leak on the intake side (I prefer the simple solutions) Smile

    

15Back to top Go down    Re: Engine popping on Mon 29 Sep 2014 - 8:09

Be made

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BarryM wrote:Well they've not been checked for a few years so I couldn't say for sure, the bike doesn't do more than a few thousand miles each year so my maintenance schedule isn't quite as thorough as it might be Embarassed

I'm still thinking it could be an air leak on the intake side (I prefer the simple solutions) Smile
Doing the valve clearances is critical to a smooth running K. IMHO setting them IS the simpler check to do

    

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