Some good mechanic will know the answer to this....

[KEITH KRAUSE]

Several weeks ago, my bike was popping and sputtering badly. I noticed that even after running for several minutes, pipe #4 wasn't even warm. I also noticed that if I pulled the plug wire from #4 while it was idling, it had no effect on the way it ran.

So.....I cleaned carb #4 really well and put everything back together. The problem seems to be solved and it runs fine....but: Now that it runs fine, I notice that if I pull the plug wire from #4 while it is idling, it will die immediatly.

That leaves me completely stumped and I'm suspecting that maybe the problem had nothing to do with the carb itself but, rather, something else. So my question is: Why would the engine not die when I pulled the plug wire from a non-functioning carb...but will die when I pull it from the carb, now that it's working?

There's got to be a simple answer but I can't imagine what it is. I'm hoping someone can help me out because I feel like I really may need to know. Thanks, all!:-D

If #4 carb was running rich due to a loose jet or blocked air passages, then that rich mixture would foul the plug. You'd have no spark to begin with so pulling the plug cap off would make no difference.
Now that the cleaned carb is allowing a correct mixture and therefore a good spark, pulling the cap off forces it to run on three cylinders. Many bikes will run on three or even two cylinders if you keep throttling them, though not well of course. Many other bikes won't run at all on three cylinders because they're not in the best of tune to begin with or are still warming up.

[chuckycheese]

Thanks

Thank you, Keith. That seems to make a great deal of sense!!:-D

[tateG]

Have you taken the plugs out and cleaned them since this all happened? I have noticed plugs in bikes can make a much more substantial difference in the way the motor runs than a car engine.

For example, a friend bought a super nice low mileage Honda CB350, could not get the thing to start. Checked the carbs, gas flow, and even checked the spark; all seemed good. Called my motorcycle mechanic friend and he told me to get two new plugs and it would fire up, and sure enough he was right. The old plugs looked ok and had spark, but I guess it was weak and wouldn't fire the bike. New plugs and it fired off immediately, no other changes.

ANyway, new plugs are worth a shot. I know my bike can idle on three cylinders, but that problem was due to a plug boot that was loose where it connected to the wire.