Just bought a new carb for my sons 250 and cant seem to get it to where it has good throttle response. It boggs really bad on the low end and once it get moving it it gets better but still not what you call peppy. It still seems like its lacking power on top end. I turned the mixture screw all the way in and backed it out 2 turns it would start without hitting the throttle but poor throttle response. I backed it out another half turn and it seem to have got worse so i screwed it back in 3/4 turn and it might have helped it a tiny bit but not much. Just cant seem to find the sweet spot. Does any body no what might be going on here. Engine does not smoke. The hose from carb to breather is missing also.

 

If it is a Keihin CVK32 carb then the low speed Fuel Screw setting is 1 3/4 turns out. Should have 3-6mm free play in the throttle cable at the lever.

Also may need to check the jets if problem continues. Main Jet is a 138 slow jet is a 38 and the needle jet is 4.0/3.4 with a jet needle N8TT.

Spark plug should be a NGK-DR7EA

This is from a 2004 service manual. The 300 and the 250 use the same carb but have different settings and jets.

Hope this helps

SJ