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???

Apart from a whole host of other fuel/air ratio problems, you might be running a too hotter spark plug. Go for a cooler grade and then find out what colour it is.

The higher the number, the hotter the tip.

ya i just go into the store and tell them the make and model of the bike and take what they give me i tried the 10 $ plug and the 4 $ one both didn't work i'll have to find out tho thanks