I have a 2000 400EX. I had a wiseco piston installed and a top end rebuild at the same time. I have about 600 miles on the rebuild. The valves tick until it gets warmed up. When I first start it, it puffs a little smoke. But soon after it runs clean. Someone mentioned to me that there may be some circuit that controls fuel mixture when the engine is cold. I dont know if that is true. Is it possible that after breaking in a top end that instead of the gap in the vavles getting looser, could it get tighter and the valves not be closing completely? The bike runs great once its warm. But Im concerned about the cold start smoke. Plus the ticking until its warm.

 

What color is the smoke? If it is blue then you probably have a valve seal problem which is no big deal.

 

yes you have a valve seal out but no worry i have one out on my 440 also and it runs great!