Forum bmwbike.com

My R69S starts on the first kick and idles normally until it is warmed up. It just starts speeding up at some point for some reason. The bowden cables are slack and the slides have not moved. Can anyone tell me what the problem could be. I may have balanced the carbs while the engine was not at the normal operating temperature....could this be the problem. Everytime I start with the engine cold, everything works fine. If I shut the engine off once it has started speeding and start it again, it comes back immediately to it's fast regime. If I remove each HT cables alternatively, the RPM goes down to normal in both cases on one piston but as soon as both are on, the RPM shoots up.

It is normal for the engine to idle faster when hot than when cold, due the oil becoming hotter and thinner.

And it is normal for the engine to idle half as fast on one cylinder than on two, as the live cylinder must work against the compression of the dead cylinder.

When the engine is hot, remove each spark plug cap and adjust the idle speed screw on the running cylinder so that it barely runs without dying. Repeat on the other side. Now when both cylinders are idling, the rpms will be proper. The rpms at hot idle should be fast enough so you are not afraid the engine will stall at a stoplight. When cold, this idle may seem a bit slow.

Sounds like the centrifugal advance is sticking. Check the springs, and be sure the weights move freely. Chances are, one of the springs are broken/missing. Hope this helps.

Thanks Allan, it works like a charm now. All I have to do when cold is to give it a little twist to make up for the slide height when I start it.

Thanks Mike. It turned out Allan's directions cured the problem. I do have to change my advance mecanism as the right cylinder is off by about 4 deg (retarded). This situation emits fuel residue at the exhaust (at least I think this is why the right cylinder is smoking slightly!)

Same problem for my buddy's R60 was a slight air/vacuum leak at the cyl head flange gasket--diagnosed with help from Bing. They wanted to grind the carb side flanges for $$, however Vech recommended a glass table top to verify flatness. Flat they were so a thin layer of non-hardening gasket compound when on the gaskets...solved the problem.