BMW K bikes (Bricks)

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1Back to top Go down    Backfire on Wed Jul 19, 2017 12:54 pm

BooG

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My K75 has developed the habit of occasionally backfiring on decelaration in 3rd gear....am |I right in thinking its related to the TPS? If so, what's the cure?
Thanks. Shocked

    

2Back to top Go down    Re: Backfire on Wed Jul 19, 2017 1:12 pm

Point-Seven-five

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Are you completely closing the throttle. My k75 bikes both backfire if I don't close the throttle completely when coasting. Both bikes have properly adjusted TPS and tight exhaust systems.


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Present:
1994 K75RT
1994 K75S
1992 K100RS

Past:
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

3Back to top Go down    Re: Backfire on Wed Jul 19, 2017 1:46 pm

BooG

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Possibly....I'll keep an eye on that, to see if I am shutting down the throttle completely.
Thanks for the reply!

    

4Back to top Go down    Re: Backfire on Wed Jul 19, 2017 1:47 pm

BooG

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Wow....I just became a Gold Member....that's a little bit "Austin Powers", no?! Laughing

    

5Back to top Go down    Re: Backfire on Wed Jul 19, 2017 3:06 pm

92KK 84WW Olaf

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@BooG wrote:Wow....I just became a Gold Member....that's a little bit "Austin Powers", no?! Laughing

No, its John Cleese. Austin Powers comes next........


__________________________________________________
1992 K100LT 0193214 Bertha Alaska Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 58,645 now 84,600 miles
1983 K100RS 0011175 Fricka 29,000 miles Damn K Pox
    

6Back to top Go down    Re: Backfire on Wed Jul 19, 2017 6:11 pm

robmack

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K75 may backfire as a result of a maladjusted TPS. It may also backfire because there is an air leak in the exhaust system, usually within the first 50cm (20") of the exhaust. That means either copper gaskets in the exhaust ports are leaking or the joint between the headers and muffler is leaking. Check these areas.


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Robert
1987 K75 @k75retro.blogspot.ca
2011 Moto Guzzi V7 Racer
http://k75retro.blogspot.ca/
    

7Back to top Go down    Re: Backfire on Wed Jul 19, 2017 6:37 pm

MartinW

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Incorrect mixture setting can also contribute to backfiring.
Regards Martin.

    

8Back to top Go down    Re: Backfire on Wed Jul 19, 2017 7:07 pm

Woodie

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I found that I tended to backfire more after I turned 50....oh wait..that's thread drift. Sorry


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1985 K100RT
52667
"Keep your stick on the ice. We're all in this together." Red Green
    

9Back to top Go down    Re: Backfire on Wed Jul 19, 2017 8:30 pm

AL-58

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My wifes K75s always used to backfire more when the gasket between the headers and the muffler started to fail.


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'87 K100RS/HRD sidecar (1100 motor)sc25
'92 K100RS-16v (Paint it Black)

'87 K100RT with Paralever backend

"When I'm too old and too foolish to handle a sidecar I'll buy a Sportsbike"

    

10Back to top Go down    Re: Backfire on Wed Jul 19, 2017 9:04 pm

TacKler

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@Woodie wrote:I found that I tended to backfire more after I turned 50....oh wait..that's thread drift. Sorry

You're not the only one.

My 75S has backfired for most of its life in similar circumstances. The TPS appears fine and so does the mixture (Thanks Martin). Quite possibly the exhaust to header gasket, as suggested but not going to pull the headers off just for that.

I don't have a problem with it. It sort of sounds kool, a bit like a hot cam Rolling Eyes


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Red 1991 K75S
    

11Back to top Go down    Re: Backfire on Wed Jul 19, 2017 10:02 pm

92KK 84WW Olaf

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@AL-58 wrote:My wifes K75s always used to backfire more when the gasket between the headers and the muffler started to fail.
roundel roundel roundel

I think CF needs to move this thread to the humour section.


__________________________________________________
1992 K100LT 0193214 Bertha Alaska Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 58,645 now 84,600 miles
1983 K100RS 0011175 Fricka 29,000 miles Damn K Pox
    

12Back to top Go down    Re: Backfire on Thu Jul 20, 2017 7:28 am

Holister

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Just my thoughts, but I think if you've got backfiring, its a sign of unburnt fuel. The TPS not functioning or leaks in the header/exhaust system will be just contributing to igniting that fuel in the exhaust system as it escapes.
Quite a few here have disconnected their TPS to give a smoother engine braking experience. Not heard too many complaining of backfiring in these cases.
I'm thinking that on top of checking you have a tight exhaust system and your TPS is functioning correctly, that you also try advancing the ignition timing a smidge but within limits.
Another cause for unburnt fuel could be tight exhaust valves. My Old Girl (K100naked) used to go off like a rifle when backing off in 3rd and 2nd and usually as I was trying to quietly approach home. Exhaust valves were very tight. Backfiring disappeared as soon as that was put right. Best to check your valves anyway to avoid valve damage if this is the case.


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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
    

13Back to top Go down    Re: Backfire on Thu Jul 20, 2017 10:47 pm

MartinW

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Easy way to check for exhaust leaks is to stick the hose from a vacuum cleaner one of the ones that you can reverse to blow, up the exhaust and loosely seal it with a rag. Then spray the exhaust joints with a mixture of detergent and water. If you see bubbles ( soap bubbles not Michael Jacksons Chimp) you have a leak. Alternatively you can use a compressor, you could probably even use one of those cheap $10.00 12v tyre pumps.
Regards Martin

    

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