hello i have a yz 125 2 stroke dirtbike and i have never rebuild an engine before but i did this summer put a new stater and flywheel in all new seels gaskets piston ... it worked out great had a really nice ride for about 3 hours last week then the sparkplug was burnt out it was black on the bottem but not to bad this weekend i put a new plug cap on because the old one was a little cracked but i went for another 3 hour ride and it happend again i was told at my local yamaha dealer that it might be the carb jets does anyone know how i could find out how to set them the right way or if thats even the problem???