Just bought a 92 lt250r it was bored 40 without a lid on air box. It runs like crap, so I checked the main jet size it's a 260 stock. Could that be the reason the quad hesitates when I ride it?

 

It could be. Can you do a plug chop? I done have an LT or the manual for them anymore, is it 260 stock? Have you tried with an air box lid (tape could work in a pinch.)

 

I put a new plug in b8es and checked it after I tried to ride it but plug looked fine.. Yeah the 260 main jet is stock and the guy I bought it from bored it 40 over with carbon reeds and pipe.. I put a piece of cardboard in place
Of airbox lid. I'm not sure how high I should go with main jet and pilot? My pilot is 30.. My quad has powervalves too.. Not sure if I should play with that

 

Well, it will run poorly if the power valve is not working. Piped you may need to go up a couple of.sizes on the main, possibly the pilot too. What part of the power band does it fall flat?

 

Power valves are ok.. I'm not sure how high I should increase the jets? 280?

 

If 260 is stock, 280 would be a decent next step. Again, where does it fall flat? Pilot is responsible low in rpm range, then needle, then main. Engine porting and exhaust also can change the power characteristics. Is there anywhere it runs well?