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Matt, Mechanical Engineer
Category: BMW
Satisfied Customers: 21599
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a bmw r850 c motorcycle,it misfires at constant

Resolved Question:

I have a bmw r850 c motorcycle,it misfires at constant speeds, from low down at 20 mph to high up at 70 mph, any speed in the range. power and acceleration is good. have changed oil.oil filter, air filter, plugs, plug leads, coil, taken tank off and cleaned it with new fuel. checked intake hoses. taken it to bmw garage on a diagnostic machine and they say its ok but its not.answers please
Submitted: 1 year ago.
Category: BMW
Expert:  Shantal-Mod replied 1 year ago.
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Customer: replied 1 year ago.
No I have not found the answer, The bike has been put on a computer but it found nothing wrong, although the bike is 16 years old it is in very good condition and has been well maintained with only 34000 kms on the clock. It only has this fault when the throttle is just starting to open,no matter what the constant speed
Expert:  Matt replied 1 year ago.


This sounds like a lack of fuel and could be a lack of fuel pressure from the electrical pump at the tank.

1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,

Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

Matt, Mechanical Engineer
Category: BMW
Satisfied Customers: 21599
Experience: BEng hons Mech engineering, in auto industry 22 years
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