Motorcycle Repair: 73 honda running rough, carberator, mechanical advance

Question
so i got this bike (honda cb350 1973)form my bro. last summer. it ran almost perfectly then, but suddenly stopped working. this spring i decided to get it up and running again and after much tinkering found that there was a small rock stuck in one of the jets of the carberator. i cleaned the carbs and rtebuilt them and the bike runs now, but roughly. first off, the left points spark pretty much on every revolution, while the right don't spark at all. because of this it makes the timing on the left a little sparatic, seeing it while timing with a strobe. but the strange part is, when i get the timing as close as i can, the bike will work acceptably well, but after about 5-10 miles the left cylender timing will get off, and the bike starts to jerk and sometimes backfire. and even stranger still, sometimes when i'm adjusting the timing on the left after all screws and bolts are tightened, the rpms will kick up to 4000 (in idle) and i'll check with the strobe and the left timing has increesed dramatically (15-20 degrees) so i'll stop the engine, wait a few minuets, start it again and it will be back to normalish. while all this is happening the right timing stays faithfully on it's mark. what is going on here? thanks for your help.

Nick

ps this being my first bike and having nothing to compare to, how do i tell if the engine is too hot?

Answer
Nick, I think primarily that your problem is stemming from a bad condenser and/or loose condenser lead for the left side. Arcing points are a dead giveaway that the condenser is not operating on that circuit.

After you check the condenser leads/replace the unit, remove the point plate and check the action of the mechanical advance unit. It should spring back against a gentle twist of the point cam, by hand. If not, then mark the cam and remove it from the advancer unit. Clean the shaft, lubricate it and reinstall the point cam correctly.
Lube the point cam up lightly and then reinstall the point plate after you have inspected and cleaned the point faces carefully. Reset the gaps and ignition timing to stock specs and watch for any more arcing.
Dirty points will arc a lot to, but not on every opening.

A good connected condenser, clean points, working advancer and proper settings should get you back on the road again.

350 carbs are known for diaphragm failures and need to be cleaned and adjusted carefully to function correctly. Be sure to pay close attention to the synchronization when you are done with initial settings on idle mix and speed screws.... all this AFTER you get the timing sorted out.

Bill Silver