Dirt Rider Magazine

I bought my 15 yr old this 2004 RMZ 250 last year. My first experience with a 4 stroke DB. It ran great until it began smoking about a month ago. I broke it down and found the exhaust cam lost its fit, the piston had a piece broken out the top and oil ring damaged. I never found the piston peice(checked bottom end best I could with out splitting the case). The cylinder was fine. Bought a wiseco top end kit and new head. Adjusted valve clearances to spec and set valve timing. Now the bike is running hot. It will not even idle with out the choke on. After running for a couple of minutes it gets hot starts pouring radiator fluid. I pulled it all the way down again but found nothing. Put in fresh fluid(50/50) and it still runs hot right after starting. Do I have an air leak somewhere? Can the base gasket be put on upside down/not sealing? I'd rather not take it to a shop but not sure what to do next. I can trouble shoot 2-strokes in my sleep but a little lost with the thumpers.

do u have the boysen are pc cooler on it are that one thing so u can change the oil with out draining the radiator fluid these bikes have a problem over heating iv herd that putting engine ice are bigger radiators in it