I've got an old '86 KDX that's been bored to 240 (long before I got it). Since I can't afford to spend much on it, I'm hoping to get a good diagnosis rather than do a bunch of work that, while clearly would be better to do, isn't strictly necessary. Also, the bike only gets ridden a few times a year.
The symptoms:
It was running great in the morning, and I rode for about fifteen miles to man a checkpoint at an enduro. At the end of the day, it started right up, but ran very rough at anything between idle and full throttle. It seemed to have plenty of power at full throttle, though. I put in a new plug, which didn't change anything, and it gets me back (downhill) to the pits. Several months pass before I can get back to the bike (don't ask...).
I pulled the carb, top end, and airfilter, cleaned everything except the kips valves, checked the jets and needle and float, and expected that it'd be good to go. But no such luck. It started right up, still ran very rough at anything but full throttle, but this time it died after about two minutes of riding. It wouldn't start or even burp. I shut off the gas, let it sit a few minutes, and it repeated - will start up nicely, run briefly at full throttle, then die.
So I can't figure an explanation for these symptoms - it's not really what I'd expect with a stuck float or bad float level; it doesn't seem to be a clogged air passage or problem with the carb slide; fuel starvation doesn't seem to explain the rough running; it has 130+ psi compression; the piston showed no visible damage; and I don't see how a problem with the kips system could have this effect. I don't know whether the coil, or the CDI could fail like this, or if there's some issue with the stator coils that could do it.
I'll probably try to get new seals for the kips, and clean them all up, but before I spend money on a new piston etc. or replaceme any the electrical components, I'd like to have some reason to believe that would clear up my problem!!
The symptoms:
It was running great in the morning, and I rode for about fifteen miles to man a checkpoint at an enduro. At the end of the day, it started right up, but ran very rough at anything between idle and full throttle. It seemed to have plenty of power at full throttle, though. I put in a new plug, which didn't change anything, and it gets me back (downhill) to the pits. Several months pass before I can get back to the bike (don't ask...).
I pulled the carb, top end, and airfilter, cleaned everything except the kips valves, checked the jets and needle and float, and expected that it'd be good to go. But no such luck. It started right up, still ran very rough at anything but full throttle, but this time it died after about two minutes of riding. It wouldn't start or even burp. I shut off the gas, let it sit a few minutes, and it repeated - will start up nicely, run briefly at full throttle, then die.
So I can't figure an explanation for these symptoms - it's not really what I'd expect with a stuck float or bad float level; it doesn't seem to be a clogged air passage or problem with the carb slide; fuel starvation doesn't seem to explain the rough running; it has 130+ psi compression; the piston showed no visible damage; and I don't see how a problem with the kips system could have this effect. I don't know whether the coil, or the CDI could fail like this, or if there's some issue with the stator coils that could do it.
I'll probably try to get new seals for the kips, and clean them all up, but before I spend money on a new piston etc. or replaceme any the electrical components, I'd like to have some reason to believe that would clear up my problem!!