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My 1989 BMW R 100rt is coughing once or a few times at around 3000 RPM. It is only under acceleration and only in first and rarely in second. And it seem to be over one I am cruising. But it seem to be more of a problem when it's cold then warm. but it also doesn't happen when stationary or in the higher gears.

Give her a tune up. Check the basics.

1989 USA models were under full control of the EPA and mandated to run on as lean a mixture as they could stand to meet the legal requirements in place at that time. They were so lean (and hot) that it really spelled the end of the Airhead engine. Thus the move by all makers to liquid cooling and computer-controlled fuel injection.

Thus a 1989 engine with stock jetting cannot stand even the slightest of air leaks, or the tiniest bit of varnish on the needle or needle jet... in short ANYTHING that makes the engines run one tiny bit leaner.

If not already done during your ownership, then I'd highly suggest replacing the rubber intake hose, the #45 slow speed jet, needle jet, and carb needle. If you want better performance and engine longevity, then you can bump the needle jet up one size. I bumped my 1988 RS from 2,66 to 2,68 on the needle jet. Not only did the performance radically improve but the head and exhaust temp dropped.

Then, strobe time the engine at high RPM using the "F" mark. That's the only way to insure the ignition is correct on vintage engines.

Hope this helps.

What Wobbly said!!!!

George Ryals wrote: ↑Fri Jul 06, 2018 3:46 pm What Wobbly said!!!!

Also clean those little holes at 6 o'clock just near the butterfly. Remove the mixture jets (note how many turns to closed first) Spray carb cleaner into the holes and thread some fishing line into the holes to loosen anything then spray again.

Duane would always say that to spray was only half the job.

Remember!!! When spraying carb cleaner in holes or anywhere, WEAR SAFETY GLASSES!!

Thanks for reply and advice. The problem is getting worse, and I now realize it must be a gearbox issue, not an engine problem. There is mechanical clanking/banging noises accociated with the problem. Only in 1.st gear.