your going to hate me 500atp for correcting you again, but trailblazer is a 2 stroke. no valves.

 

After reading the replies to your post I would not listen to the non 2strokers that tell you to "bore big" That it waisting your cylinder.But if you plan on keeping the 250 and your son has enough experiance to ride a modded 2stroke (if you mod it like I say it will run with the 350 Warriors and 300exs)
First get the cylinder ported (a must for flow) then get it bored only enought to clean up the cylinder(ussually only .020 )
Then get you the HPD pipe,the good MT silencer and thier recomended clutch kit
add a K&N air filter and proper jetting and hang on.
Now if you wanted to drop about $1600 on it HPD makes a reed valve conversion kit that will get the little 250 where it will run with any of the 400s.

 

definetly do not go big bore its a waste because 2 strokes will not benefit from it. just take it apart and get it bored 1 size and replace your piston with a wiseco piston kit...and if u have a lil extra money get a new exhaust and port it

 

FTWFLH tbsleeper,

Thank you and thank you to all I talked with rick ritter and were going to go with the stage 1 kit he has with a bore and piston. I think this is the best bang for the buck. thanks again for helping.