hesitation, 250es

[BIGREDMAN]

even after completely rebuilding and tuning my carb and replacing the plug my big red still has some serious hesitation. once revved up the engine runs fine but from idle i cant gun it too hard or the engine will cut out. bad timing?

[bones200x]

I would check valves.
Does your carb have a manual slide or vacuum slide?

[BIGREDMAN]

honestly i dont know what that means. if you could explain it i know the carb fairly well. what does the slide do

[bones200x]

The slide moves the needle up and down. It is UNDER the cap on top. If it is mechanical, it would have and arm to move it. If it is vacuum, it would have a big round rubber peice on top(under the cap).

[BIGREDMAN]

its mechanical.

[bones200x]

This is an old trick a tech taught me. Still is used today too.
Back off the idle screw untill it is NOT touching the throttle. (may have to remove carb.) Make sure you only have VERY little play between the arm and slide. The slide should move almost the same time the throttle plate does. Usually takes a flat tip screwdriver to adjust (on throttle cable side).
It CAN be timing , Vacuum leak, Or carb stopped up or out of adjustment. Most of the time, Timing won't be off. if it is, then usually CDI box.
Check for vacuum leaks and adjust slide on carb. Have you tried adjusting pilot screw? Maybe too far out/in...

[Liquid-Darkness]

Maybe the top end has no guts left? Check compression maybe? Perhaps this new good fuel flow is too much for the piston bore and rings. Anyone think this is possible?

[BIGREDMAN]

well, after putting everything back together the bowl started leaking gas all around the top so i think all my seals are worn out so im going to rebuild the whole thing with all new jets and seals. On top of that my air filter is trash and after removing the carb again just today i found debris from the foam part of the filter. i dont think theres anything wrong with the engine its self. i might check the compression sometime just to know. it doesnt burn oil or smoke or show any signs of blow-by so i would imagine the piston and ring are just fine. as for the valves and their adjustment i dont know how to check any of that but it doesnt clatter or make any valve noise under any condition. seems good to me....?

the original pilot screw was stuck and i had to drill it out, the head of the replacement screw broke on installation so im ganna have to do some work on that. would that have this dramatic of an impact on how well it runs?

thanks for the help btw

[dads]

Check the carb pilot screw setting.
I know on the 250sx if it's off it will hesitate

[bones200x]

Now we have a better idea. If you can't fix the pilot screw, the 250es big red and 250sx have same carbs. BUT they use DIFFERENT jets. I just put a 250es carb on a 250sx. The carbs was IDENTICAL. Just had to change jets. The air boxs and boots are different also.
The reason of replacing carb....PILOT screw broke off. It was the second time so it really screwed the carb up this time. I can't remember what size the screw is to retap the hole.

[BIGREDMAN]

my threads are still good so i think im ok, we'll see tho. i think it leaks a little gas tho now so i might seal it with some locktite or something. how much does a carb cost?

[BIGREDMAN]

so i rebuilt the carb with new seals and jets. any reason it should be running worse than ever now? doesnt quite make sense