2000 kx80 engine modification

[JonV]

my son races both the 80 and supermini classes. last week we had a catastrophic engine filure, so now is a good time to make this thing rip. next year will be a new bike, and this ride will most likely become a full supermini. he rides am/exp and is a mid-top powerband rider.

we will need to replace (or repair) the cylinder.

what would be the best motor combination for this bike and be ama legal? (or should i ditch it and get a kx85)

mods now in place are a pc pipe / shorty silencer,boyesen pro series reeds, mild port cleanup, 27.5mm bore carb.

will the kx85 top end assembly interchange or is an overbore / stroke setup better. are PVL ignitions worth the cake or will an 85 black box net any gains

any help is greatly appreciated

 

[ACS]

My boy has a 2000 KX80 and I would sell. The new YZ85 flys and the new RM85 looks very good on paper. The KX85's are a bit better than the 2000 but not that much. I watched the new YZ85 in action and I was impressed. To get a KX that fast and handling as well would cost a lot. You said your boy is a top end rider and either the CR or YZ I believe is better for them.

 

[JJmxr]

Have Eric do his porting magic,and have him do a AMA legal 2mm overbore. He did it for my sons 98 YZ80, and it rips. As a matter of fact he raced against a bunch of 02 YZ85s last weekend, and not only did he pull a great holeshot, but up a big hill they couldn't pull him. Finished 3rd OA. You could also have him take it up to 100cc if you want a decicated supermini. I believe RPM has a 105, and 112cc kit, but for big bucks. For about 300 bucks (including a piston kit!) Erics work is hard to beat. Good luck.