just bought it.87 honda 250r,,bored 40 over pro desigh cool head. 10 hours on motor,fmf full system,uni filter.from where i bought it different elevation 1500feet higher.main jet 145,pilot 48,idle runs find,midrange good,top end good.from idle to midrange it boggs(hesitate).midrange to top end good.plug little wet and black.any help would be greatly appreciate.

 

adjust your air mixture screw out just a little maybe a 1/4 to a 1/2 turn maybe more.

 

tried that. still not good

 

If you went up in elevation try a smaller pilot jet.