1975 honda xl250 help needed

[johndeerekid]

hello everyone, my names wesley and i am new to the site. i currently own a 1975 honda xl250 that me and my dad have restored. the bike is awsome and runs really good but we are having some problems with it. when the bike is cool it starts up first kick and runs great! butt as the bike gets warmer the bike really starts to bogg down and it eventually just stalls out and wont start whatsoever. if you let the bike sit for about 20 minutes and cool down it starts right up first kick and does the same thing over and over. me and my dad have no clue whats wrong but we are thinking maybe the coil. we have put brand new points and spark plug in it, we cleaned and reset the carb and float, we put a brand new battery in, and i brand new air filter. we have no clue whats wrong so please help us:) thanks, -wesley.

 

[dirt bike dave]

My first guess is the valves are set too tight.

Basically, as the motor gets hot, the clearances disappear and the valves stay open a little. This will kill your power and make it impossible to start.

With wear, the valves tend to get tighter over time as they recess into the head.

If the valves are set loose enough, my next guess would be the stator is going bad. This can often be heat sensitve and very hard to diagnose.