250-500cc power band problem

hi there i have a 96 husky wr360, had a full rebuild. crank, rod, piston, every bearing in the engine replaced with new. new reeds cleaned the carby, replaced the spark plug, coil and lead.

ok so here is the problem start in fine no problem. warm it up for about 5-10 mins, runs fine power band come on beautiful. after riding it around for about 15-20 mins the problem start to happen power band dosent come on, bottom end runs good but soon as it should come into band, nothing happens.. makes a big brrrr noise and donts want to move just satys at the same speed.. when this happens blows more smoke then normal..

if anyone could help me out would be much appreciated..
Cheers

Have you tried a new spark plug?

Maybe a Crankcase seal!

cdi was going bad on my bro's cr250 did the same thing.

Usually it would be fine untill 10-15mins like your saying.

If you have a manual there may be a multi meter test for your cdi.



Though if it were the cause, its weird that the problem just popped up after your rebuild.

remove the hts cover and run and warm up bike as usual, once the problem occurs disconnect the linkage at the upper power valve actuating arm and wind the throttle if the bottom actuating arm moves then the problem is in the exhaust valve mechanism you can check this for free movement by physically moving it, may be binding when hot.
other than that you will have to do the usual back tracking to nail down the fault.reeds, jetting, seals, electrical and vaccum.
if you have a decomp head check that too.
hope this helps.