Bob_
CB750 Member
Hi, I have an 81 cb750c with 3,800 miles that I bought as a winter project but I cant quite get it running right. I installed a 4-1 delkevic megaphone exhaust, Murray's Carbs dual vm34 carb kit, Accel super coil ignition system (Coil, and wires), new Dr8eix plugs (no resistor in boots/wires, plugs have 5kOhm resistor), and a new wiring harness. The cyl 2-3 running cold issue however still persist.
Backtracking a little bit, when I installed the new wiring harness, all 4 cylinders started firing correctly. The next day though, I was about to go and fine tune the carbs because I though it was running rich, (Fouled plugs, soot in exhaust, lugging with idle at 1200, only idled smooth at 1500+, and revs hanged if slowly brought up to 5-7k rpm). However, before I could even begin tuning I noticed that 2-3 were once again not firing. (The fouled plugs were cleaned prior).
At this point, I'm kind of at a loss as to what it could be. For further troubleshooting I have switched the spark units with no change, checked all connections, and got 150psi on all cylinders with a compression test, and gapped the pulse generator to 0.013. Timing also appears correct by eye and as stated, 1-4 fire fine. The only 2 things left that I can think of are the pulse generator (I hope not because they don't exist anymore as far as I can see) or the valve clearance, but that seems unlikely due to the compression.
Any advice would be greatly appreciated as this issue is driving me mad.
Backtracking a little bit, when I installed the new wiring harness, all 4 cylinders started firing correctly. The next day though, I was about to go and fine tune the carbs because I though it was running rich, (Fouled plugs, soot in exhaust, lugging with idle at 1200, only idled smooth at 1500+, and revs hanged if slowly brought up to 5-7k rpm). However, before I could even begin tuning I noticed that 2-3 were once again not firing. (The fouled plugs were cleaned prior).
At this point, I'm kind of at a loss as to what it could be. For further troubleshooting I have switched the spark units with no change, checked all connections, and got 150psi on all cylinders with a compression test, and gapped the pulse generator to 0.013. Timing also appears correct by eye and as stated, 1-4 fire fine. The only 2 things left that I can think of are the pulse generator (I hope not because they don't exist anymore as far as I can see) or the valve clearance, but that seems unlikely due to the compression.
Any advice would be greatly appreciated as this issue is driving me mad.
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