cr250 or rm250 on blaster???

would probably fit but the 250's have huge carbs. i believe they have 39 or 38mm stock. the most a blaster needs is a 35mm
 
cr is 87 and the rm is 91
The carb off the 87 might be small enough. The reason why I asked it like dave said the newer one use a 38mm. Best thing to do is measure it I:I

I'm geussing your blaster is fairly stock? A 34mm is more then enough, even that it a bit too big for a stock port lay out / jug / 200cc blaster.... a 36mm or 38mm will run like sh*t..
 
250 carbs are to big for a stock motor...i know for sure a 1989 Honda CR 80 carb will fit its a bit bigger than the stocker like 28mm i think that way would work best if you have your heart set on a new carb that is bigger