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1988 K75c


SteveSardone

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My son just purchased a 1988 k75c. We changed all the fluids and spark plugs. Starts and runs great except for hesitation and stumble when first twisting the throttle. I own and wrench an RT but this is a first on a K bike. Any suggestions on where to start? Is there such a thing as a TBS on these bikes? Where is the fuel filter?

 

thanks for anyone's help,

 

Steve

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Yes, the throttle bodies can be synchronized with a manometer and the brass slot head screws on the outside of the throttle bodies. Idle should be in the vicinity of 1000-1100 rpm. Try a good dose of Chevron Techron fuel system cleaner in the gas. It will help clean the injectors.

 

The fuel filter is inside the fuel tank. Remove the four screws that hold the fuel cap on after opening it up. Remove that, and with a low level of fuel you can reach in and undo the filter from the fuel pipes. There should be a hose attached to the rear end that is long enough to take it out of the tank.

 

Frank

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Hello,

 

FWIW, I just purchased an 87 K75S. It had not been ridden much. I put about 1000 miles before changing the plugs, occasionally experiencing a very similar issue. I changed the plugs and have found that over the next couple hundred miles, the issue basically went away, to the extent that I no longer can even make the bike stutter. Maybe give the new plugs time to "do their thing??"

 

Good luck,

Neil

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I have an '86 K100 that I have had totally apart and know it inside out.

 

Change the plugs (be sure to use the ones specified by BMW).

 

As was elsewhere stated, synchronizing the throttle bodies may help. For this you need 3 vacuum gauges or 3 manometers. Also as stated, this is done using the brass screws on the throttle bodies, and NEVER USING THE SCREW ADJUSTMENTS ON THE THROTTLE SHAFTS!!! But to be honest, I have never found that synchronization caused this problem.

 

One thing that can be a problem is an air leak. There is a small rubber hose at the back of the motor on the top left side (as you sit on the bike) that leads up to the airbox. This hose has a habit of cracking and leaking air, resulting in a lean idle mixture. Remove the airbox and replace the hose if it is cracked.

 

It may also be a good idea to verify the idle mixture once you have ensured there are no leaks. Normally this is supposed to be done using a CO analyser, but here is a way to do it without one.... http://skylands.ibmwr.org/tom/tech/co-setting.html

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thanks for all the quick and good info. I will check the air hose for cracks and run some injector cleaner thru it. We put the NGK equivalent of the bosch plugs-any problems?

 

I only have a twinmax-could you give me more details on the vacuum gauges or manometer. I've read how to make one to use on my RT???

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Change the plugs (be sure to use the ones specified by BMW).

 

IMHO, "be sure to use the ones EQUIVALENT to the ones specified by BMW" A K75 couldn't care less whether its plugs were made by Bosch, NGK, Champion or any other reputable maker of your choice.

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Change the plugs (be sure to use the ones specified by BMW).

 

IMHO, "be sure to use the ones EQUIVALENT to the ones specified by BMW" A K75 couldn't care less whether its plugs were made by Bosch, NGK, Champion or any other reputable maker of your choice.

 

Autolite 4163 plugs work fine in K bikes. However, they don't seem to last as long as Bosch plugs so I replace them at 10k vs. 15k for the Bosch.

 

IF the bike has sat for a while (common with used bikes as people let them sit for a while before getting around to selling them) then it's not a bad idea to get some Chevron Techron concentrate (not the Chevron FI cleaner) and run a half bottle of that through the next two tanks. This can do wonders do a K that's been sitting for an extended period of time - and certainly can't hurt.

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