Vintage BMW Motorcycle Owners

Hello, friends. I have a BMW R12 and it has no power while driving. He doesn't go as briskly behind the throttle and into revs. What can it be and what to look at? thank you for all the advice.

Precisely setting the timing on an R12 is challenging without dissembling the engine and stamping real timing marks (in the exact correct position) on the front of the flywheel, that are visible through one of the large holes on the crankcase's right side.
And then, R12's can also suffer from differential timing if the internally eccentric ring, (that causes the points to open) is worn badly. Without visible reference marks on the flywheel, as to where Top dead center is (to check valve clearance) and 9 degrees BEFORE top dead center, (to check where it should fire, at idle, with the timing fully retarded,) twice in a row to see if you have differential timing of the left versus the right cylinder. A stock R12 has NO timing marks. In effect, your guessing, trying to tune it by ear, concerning where it fires, in relation to 9 degrees TDC and where it is firing when fully advanced.

But for the time being, if his R12 seems to have no power, (I assume that he does know that if he does not advance the timing when taking off, the engine will not develop any power) it could simply be that due to advance cable adjustment, it is not advancing far enough to produce any power. Hard to say, without the bike in front of me to test and see where the timing is set, and if it has a lot of differential timing, (which robs a lot of power).
In order for any BMW twin to run correctly, EACH cylinder, at full retard must fire a 9 degrees before top dead center. I have seen bikes (R12's and lots of others) that one cylinder fired at 9 degrees and the other one was WAY off, sometimes firing at top dead center or way off in the other direction, maybe 15 degrees before top dead center.
This will make the engine vibrate excessively and cause one cylinder to run MUCH hotter than the other.

OOPS.

I forgot to post photos of my R12's.
This is my 1936 R12: This is my 1941 R12

Thanks for the advice, you were right it was bad timing. I adjusted the timing and the engine runs like clockwork. Otherwise, you have very nice machines, thumbs up