let me start off by saying, that i am a long time reader, but have never posted until today. I HAVE SEARCHED EXTENSIVELY. all over. i have done multiple fixes and changes. but, here we go...
I road race in a mini bike series. kx65's are ultra popular and competitive due to their cheapness, speed and weight. I have a kx65, my frineds have kx65's, everyone has kx65's! lol
My kx65 however seems to have no top end power. I can run lap times close to 2 seconds faster on our endurance bike (which i dont own), and I can always really feel the top end pull on it. Both bikes are modded exactly the same. except one runs race gas, mine does not. I have ridden other peoples kx65's and their bikes also make more top end power than mine does.
What its doing is it feels like the top end just flattens out and tapers off right when it should be at peak power. It doesnt bog, it doesnt stutter, it just flattens out and makes no power where there should be 2-4k rpms of more power band.
MODS MADE TO BIKE
-wiseco 46.5mm piston (72cc), GENUINE keihin pwk28 carb - 132-148 main tested. float level set to factory specs, 42 pilot is golden, clip set to third position, off idle is beautiful, mid is great and will power wheelie shifting from first to second. vforce 3 carbon reeds. moose intake spacer, dent free factory expansion chamber, brand new pro circuit pipe.
-crank, piston, and main bearings have 10 hours on them. rings have maybe 1 hour on them, plug color with WOT plug chops in fourth are kinda ehhh, not dark, but not light, but i can never jet it to the point of it being brown on the main jet. i have as of today ordered a 130 main jet to try even leaner settings...color largely remains the same no matter what, power is flatter with richer jetting
things ive done to try and recitfy this issue
-new crank seals, split case and resealed it, new piston rings, performed leak down test, held pressure except for at the plugs on the leak down tester. confirmed with soapy water... jetted and jetted and jetted. confirmed timing position. 120psi of compression on brand new rings...maybe they just hadnt seated yet?, new dent free expansion chamber, new head gasket, pit free head, confirmed squish at .65mm at all four corners. squish is however tighter right at the edge due to head gasket being slightly smaller due to 72cc piston (everyone else i race with is like this too though), what else...checked coolant system, no leaks, holds water over the course of a race weekend.
last year i ran a grom, it was a pig, i wanted to get results and lap times like i had on my buddies 65, so i got a used clapped out 65 and built it.
so here we are...makes great bottom and mid power, falls flat on the top, doesnt bog, doesnt stutter, and my gearing is a little bit shorter than some peoples. i get plenty of drive off of other riders on the corner, but they catch, pass me on the striaghts. when trying to pass people, i suck up on them on the brakes and in turns, then they leave me on the straight. its been half a season of me not getting results and im getting heavily annoyed...
am i simply running out of my powerband and its being exacerbated by slightly shorter gearing? is my clutch slipping and making it feel like it doesnt build anymore power, but the motor isnt really increasing in revs...is my stator or coil going bad? who knows. im sure its engine related...
any more ideas or questions and i will immediately respond because i sit at a desk all day at work, and have pretty much unlimited internet access...
long post is looooonnnnngggggggg
my neighbors are beginning to get pissed at me for screaming around all the time doing plug chops...