R850R Back firing

[thejohn]

Hello Iv'e got a problem with my 1997 R850R 32000 mls... the throttle is surging when at a constant throttle the engine sounds rough and the worst thing it back fires on overrun. the Questions I am asking is.. what's the likely cause, and will it cause damage to the bike there appears not to be an exhaust leak or a air leak on the induction either. good job I live in North London as the locals think is the usual gun shots
Thanks in advance
John

 

[MarkShelley]

Firstly, check that the throttle cable by the right hand throttle body is correctly seated in its threaded adjuster. If it sits on the lip it runs like a bag of poop. I see you are know here so may not know about this. Most of us have done it at some stage as whenever you lift the tank it tends to happen.

 

[thejohn]

Thanks for the quick reply Mark I have been out in the fading light and the throttle cable is seated as it should be. the tank has not been of for at least 2000 miles when it was serviced by Steptoe of this parrish.

 

[Fanum]

Does it feel rough enough that it could be running intermittently on only one pot?

Mark is probably right if you have lifted the tank though.....it's a classic problem

EDIT.....you beat me to it.

Pull the plugs and see if one is fouled........run it in the dark to see if there are any 'lost' sparks on the HT side.........clean all HT connections, trace it back.


Has the TPS been knocked out of place with an errant boot?

 

[thejohn]

thanks Fanum pulled plugs about the same brownish colour both sides no spark arcing that I can see in the dark the TPS seems okay position wise and I don't think I've given it a dink with my boot. the only thing of note is I thought it's been running rich for a while and there is black soot around the rear of the exhaust pipe. and its struggling to tick over.
John

 

[Steptoe]

Could be the TPS unit is failing.

 

[thejohn]

oh dear that sounds expensive how can I be sure thats the problem
John

 

[DrFarkoff]

Well you have a Bloke above who has posted and runs a Technical Emporium of BMW "ery" in the SW15 locale

Also a used part will do the job is only £40 but if you have any doubts about being able to set it up you'd be better investing in Neil's services

<- Click

oh dear that sounds expensive how can I be sure thats the problem
John

 

[thejohn]

thanks DrFarkoff I have sent Neil a email via his web site