Forum bmwbike.com

I have a just rebuilt 1965 r50/2. The left cylinder runs considerably cooler than the right side. This is noticed at idle and after some travel. Could it be carb synchro?

It could be that the cylinder running hot has a weaker petrol/air mixture than the other. I assume your tappets are correctly adjusted and both carbs are identical, -jets-needles-needle position. Check your idle mixtures are correct for both carbs. Are both idle mixture screws in approximately the same position ie distance out from fully in (usually about two turns out from fully in) If not reset the one on the cylinder running hot to match the other and readust the idle air screw for clean idle then rebalance your carbs

Most people say that one cylinder is running too hot. What is making you think that one side is running hot? What is the difference noticed at idle, and what is the difference after travel?
If one cylinder is running hot, mixture difference or differential timing are likely causes. Unbalanced carbs cause rough idle and rough running, which you have not mentioned. Do you know how to adjust the idle mix and balance the carbs?

Unless your carbs are WAY out of synch, I doubt there would noticeable temperature difference due to carburation.

I would check the plugs and wires I had a similar problem that turned out to be a bad plug (that I replaced with a second bad plug...which made troubleshooting difficult....both would spark at idle, but would not work well at high speed). Finally, I exchanged plugs from side to side and the problem followed the plug. The temperature difference could be detected a few minutes after a ride because one side became touchable much faster than the other.

Good luck,

Bruce