F650 engine problem. Any advice?

[martheijnens]

Hi,

I ride a BMW f650 funduro, model 1999.

Currently I am in Kathmandu, Nepal, travelling from the Netherlands to Australia. The bike has problems which I describe below as accurate as possible.
1. The engine suddenly loses power, rpm falls back to stationary level but the engine stays running. This happens frequently but unpredictable. *
2. Opening the gas throttle has no effect on the rpm. Rpm stays on stationary level, engine gives some hard "bengs".
3. The only solution is to shut down and restart the engine. The problem seems to be solved but returns shortly after.
4. The problem as described appeared for the first time after a passed a major pothole. However I don't experience a relation between potholes/bumps and the occurance of the problem.
5. I had this problem leaving Sauraha (Chitwan NP) till the main road, a distance of about 6 km. The problem occurd maybe twenty times. However, being on the main road driving to Kathmandu the problem didn't occur. The next day, driving to workshop the problem was back again. So there seems to be some relation between the problem and the temperature of the engine.
6. I never had this problem before. *

Kathmandu Motorcycle Service Workshop has knowledge of European motorbikes. According to the mechanic the problem was probablt caused by failure of the carburators. So, they checked, cleaned and repaired the carburators. To no avail, *the problem persisted. Then we looked at the electric system, checked all wires and connections but found no visible damage. We measured the resistance of the sparks caps: 300 kilo ohm, which is much. So we replaced the caps with brandnew ones. The resistance of those caps was just 1 kilo ohm. I mad a testdrive again but to no avail, the problem was still there. After the testdrive we checked the resistance of the spark caps again. It was still 1 kilo ohm, so there was no electric pulse which damaged the caps. *

Has anybody a clue what causes this problem, what to do, how to go on? I am a bit desperate now!

Thanks, Mathew