Motorcycle Repair: 71 CB350 engine issue, mercury manometer, hiya dave

Question
Hey,
My 71 CB350 seems to be outputting more power from the left side than the right.  The engine idles fine when warmed up and has no issues getting up to highway speed.  I have noticed that on start up the right cylinder backfires a bit (when gearing down as well) until it warms up and after a ride there seems to be unburnt gas pooling in the back of the right exhaust pipe.  I noticed today that the left pipe seems to be making a whole lot more noise than the right and is way hotter than the right to the touch after I park it.
I am thinking maybe a mixture issue or a compression issue?
The bike had been sitting for a while and I bought it from a gent that restored it.
Damn its a cool bike and I really don't want to kill it.
Thanks in advance for any help
Cheers,
Dave

Answer
Hiya Dave!!!

Ya know... so many motorcycle techs overlook the easiest ways to trobleshoot. Carefully feeling the exhaust headers can tell alot about what the problem is. Thanks for including that in your description. A major temperature difference tween the two pipes would indicate a problem. BUT, you say the bike idles ok and you are not experiencing a problem with acceleration. Assuming the ignition timing is ok, the contact breakers are fine, you got fresh spark plugs, I would then be suspect of a carb problem. You mentioned that the bike sat for a period of time? Bikes don't like sitting... Two main issues come to mind. The carbs may be out of sync, meaning one is working harder than the other. I can sync the carbs on a twin cylinder by ear, but I highly recommend not doing so. You will need a set of vacuum gauges or a mercury manometer to check the sync. I would also suggest you acquire a manual for your bike. A '71 CB350 is a classic and should be well maintained. A manual will show you exactly how to check and set the sync. If you find they are synced within specs, then I would say that the carbs need to be removed and cleaned. Sounds like you may have a partially gummed slow jet. But check the sync first... out of sync carbs and a gummed slow jet will both produce similar symptoms. Checking the sync is less invasive than cleaning the carbs. Good Luck Dave... hope this helps!!

Jack