So I'm pretty new to this forum, but you guys seem legit. Here goes
I purchased a 73' cb750 a few months back thinking my knowledge of motorcycles was enough to keep it in running condition, I actually got the bike to run fairly strong on all cylinders, (a problem the previous owner was having), and enjoyed several great rides before a few weeks ago.
After a long ride, probably 50 miles or so, I parked the bike and upon start-up the next day, would only run on 3 cylinders, with a misfire on #4 once in a while, #4 pipe was clearly cold. I assumed a carb issue being that number 1 pipe was hot (although noticeably cooler than #2 and #3). Pulled the carbs, cleaned all passages and blew out with high pressure air. Re-installed them, now 1 and 4 fire every so often, obviously cooler than 2/3. Pulled the points plate off next, assuming electrical issue. While running with the points cover off and points set to correct gap, (0.024-0.028 in) I noticed electrical Arcing across the point gap for 1 and 4 cylinder, but not for the strong running cylinders 2 and 3.
My question is, Should there be Arcing across this gap? What is this indicative of? I tested the coil using another coil I know to be working and I get the same problem, Most likely weak spark on 1 and 4. Spark plugs are good.
