Here's the deal, I have a 91' KX250 thats been running a little odd lately. It's never been out since memorial day weekend 2002, but I have been making it run better little by little every weekend. The problem is that whenever I crank it up past 3/4 throttle, right when it hits the powerband (on the main jet), the bike starts puking out a lot of blue smoke and seems to sputter a little bit. I've been fooling with the jetting down low like the pilot and needle clip, but haven't messed with the main lately (I think I've got a 165 main in there now). Its wierd, it sounds like its hitting the powerband, but all the power doesn't seem to be there and theres a lot of blue smoke coming out. It doesn't smoke nearly that much down past 3/4 throttle, it runs fine down there. I just put in a new spark plug, and the top end has had about 30-40 hours of very easy riding on it, and it had fresh fuel last weekend. The only error on my part is that I put some 6 month old premix in with the gas (yamalube 2R), but it still runs crisp down low and through mid throttle, so that leads me to beleive that couldn't cause my smoke problem. I have a few theories:
1) the bike has been sitting so long that it just needs to be wound up a little bit. I don't run it too much on the top end and maybe just needs some good old full throttle time.
2) the main jet is too rich, or something goofy. Might need to clean the carb.
3) the reeds are toast. Although, I took them off and seemed that only a tiny bit chipped on one corner, so little that it exposed hardly any of the cage when closed.
4) the premix did this. It was an open bottle.
I really don't think its the top-end, the crank seals or the head gasket. It's got plenty of power and is still hard to kick. Also, the smoke is BLUE, not white or any other color, just blue.
1) the bike has been sitting so long that it just needs to be wound up a little bit. I don't run it too much on the top end and maybe just needs some good old full throttle time.
2) the main jet is too rich, or something goofy. Might need to clean the carb.
3) the reeds are toast. Although, I took them off and seemed that only a tiny bit chipped on one corner, so little that it exposed hardly any of the cage when closed.
4) the premix did this. It was an open bottle.
I really don't think its the top-end, the crank seals or the head gasket. It's got plenty of power and is still hard to kick. Also, the smoke is BLUE, not white or any other color, just blue.