Well, a couple of months ago, on my way to work on my CB750K5 one cylinder just quit. I was close to the Honda shop so I pulled into the parking lot and started trouble shooting while waiting for the shop to open. I noticed the smell of gas, but the float bowls were not overflowing. a more careful inspection revealed gas dripping from the drain hole at the lowest point of one of the mufflers. Ah-Ha, I said, I have gas, so it must be spark.
I pulled the spark plug on the offending cylinder and it had a spark. but a rather weak one. I pulled a plug on another cylinder and sure enough, it's spark looked a lot stronger than the dead cylinder. About then, the mechanics started coming to work, and stopped to admire the bike and helping with the troubleshooting. We all agreed it was the spark, and most likely the spark plug.
One of them went into the shop and returned a few minutes later with a new plug. We started the bike and it sounded OK. No charge for the plug...Nice guys. So with many thanks, and a self-satisfied sense of my own mechanical insight, I was on my was. It didn't take more than a few feet to realize it was still running on three cylinders, but (1) I was late for work and (2) I didn't want to embarrass the helpful mechanics or myself, so I limped to work sans a cylinder and later home. arriving with raw gas on my boot, the side of the bike and my rear tire.
Recall that the bike has two coils each with two spark plug wires, Both plugs fire each time the piston comes up - one on a cylinder full of air and gas the other at the top of the exhaust stroke. Was it possible that the coil could go bad in such a way that one plug would fire and the other would not? I have an electronic ignition. Could it be bad? Both the coil and the ignition were from Dyno, and an email to them assured me that neither option was possible. All the wiring was in good shape, so now I began to suspect either the spark plug cap or wire.
I ordered a new set of caps - I figured if one was bad, the others couldn't be far behind, even though they were relatively new. I was trying to figure out what kind of spark plug wire to buy. NAPA only had the one type of wire available by the foot, and that was the stuff that might be going bad. The conductor wasn't copper, It looked kind of like some kind of carbon impregnated fiber. I looked online, and did some research and decided a wire with a solid copper core was the way to go, but all I could find online was either sets or having to buy a 100' roll. Finally I found sold copper wire at an O'Reilly's auto parts store. So with new caps and wires, I figured I had it licked.
The first thing I noticed was how much quicker the bike fired up when cold. Obviously, I had a much stronger spark than before. The next thing I noticed was a growing puddle of gas dripping out of the same drain hole on the same muffler. Damn... I pulled the plug. The spark look great. I checked the compression. Not great, but about 100 pounds. Next I though "could it be the valves?" It didn't seem likely since gas was obviously coming in the intake and going out the exhaust, but just to be sure, I pulled the caps off and looked at the tappets. No loose nuts, everything looked fine.
I scratched my head and went back to basics. Spark, Fuel, Air. I knew I had the first two so it had to be air. Something must be plugging that carb. Off with the air cleaner. Everything looked fine. Slide opening and closing nothing blocking anything. Damn, this was getting weird. Maybe somethings really funky with the float or needle valve, though I couldn't imagine what. So, with nothing left to do that I could think of, I popped off the float bowl and found,... (are you ready for this?)... The low speed jet laying in the bottom of the bowl. Obviously not screwed in tight enough and vibrated loose.
Well, it should have been obvious... When have I ever seen raw gas running out of the drain hole of a muffler as the result of no spark? Every time I had gas running on the ground, it was always because of a stuck needle valve (well, except for a couple of brain farts when I forgot to hook the gas like back up to the tank). Damn, I felt stupid. On the bright side, The copper spark plug wires have made an amazing difference in cold starting, and I suspect in overall performance. I'll know more tomorrow when I ride to work.
Another lesson learned.
