so i'm really getting fusterated!! i have a 91 LT250r - milled head, port and polish, weisco piston, bored .30 over, fmf gold series pipe and fmf core 2 silencer, lower gearing, 38mm mikuni carb, k&n with no air box!! the motor is fresh, about 2 or 3 tanks of gas, and i just can't get the dang thing tuned!! i started high.. probably too high.. with a 460 and it fell on it's face at full throttle!! well now i've slowly worked down to a 280 and when i pin the throttle it boggs for a sec then goes but still chokes when it hits the power band!! it just does not want to rev!! also, i have not had any experience with exhaust valves (power valves).. could it be out of adjustment?? any help would be greatly appreciated!!

 

O.K., if you have an initial bog you're lean on the lower end. What is the needle set at ? How many turns out are you on the air screw ?

First off, get the main set. Try in the 240-260 range & check for plug color. I hope you know how to do full throttle plug checks. Once it runs clean up top, adjust the needle if needed, which it sounds like it needs. Middle clip (3rd) is stock. Personally, I'd set the clip in the 4th (1 notch down from stock) & see if the bog goes away. Next, turn the air screw in until lightly seated & then back it out 1-1 1/2 turns. Make sure to count how many turns in from seated it currently is.

The powervalve being stuck open would make the power really "peaky", but it would still run fine. The chances of it being stuck are pretty slim.