The bike: 1976 KZ900. Stock, 35K. Fresh top-end. Compression on all 4 excellent. Valve clearance all set and perfect. Carbs have been cleaned, quality kits installed, all specs and settings stock. Stock exhaust. Float level is spot on with new Mikuni brand needle and seat. Carb rubber mounts are new, securely tightened. Starts and runs excellent, runs good at both low and high rpm. Dyna S ignition, with three ohm dyna coils. Solid core copper wires, new plain caps. I've done the "WiredGeorge" coil power mod. New regulator. With voltmeter attached, shows no lower than 12.8 volts at start up, and an almost constant 14.25 to 14.50 volts at anything over 2,200 rpm. And that was on an extended ride with the voltmeter strapped on.
The problem: On occasion, cylinder number four will evidently not spark strong enough to fire, and at times, raw gas will drip out of the vent hole on the exhaust. I've tried several combinations of plugs, new plugs, cleaned them, etc. I've swapped plug wires on one and four many times. It will start to run good, with popping on cylinder four until the swapped lead evidently cleans up plug number four. Plug one runs fine with the swapped wire, plug four only for a short time. All plug wires, and connections are perfect on the Dyna Coil. . Swapped Dyna Coils 2 and 3 with one and four, and hand the same results. Fouling on number four, 2 and 3 are fine. Pulled the Dyna system off, put stock points with two Emgo coils on. Number four again had the same symptoms. Swapped the 1 and 4 Emgo coils with the 2 and 3, and had the exact same results. Five ohm caps on the Emgos, and all four checked, and read five ohms. I've done all of the usual four cylinder waste spark trouble shooting, and it constantly comes back to doing the exact same thing. With the coils being directly powered through a relay from the battery and the battery voltage and condition being good, I don't understand how no matter what combination of how I hook up coil number 1-4, it is always cylinder number four that is the problem. Could this be a grounding issue for the plugs? The main ground from the battery is clean and securely tightened. Stock wiring harness, but original , and since I'm bypassing most of it, and running coils though the relay, I don't see how that could be a factor. I know this is electrical, since many times when I swap the one and four leads, cylinder four starts running, even if the plug has fouled a bit. This one has me baffled. When it's running, good, it pulls strong and smooth at lower RPMs idles smoothly, and pulls very strong above 4K, Feels just like it should run.
