hey guys sorry to bother you again.the symptoms are as follows,cold or warm cosed to 1/4 trottle 2 puffs of back smoke not blue. on the ttrack orsitting in gear and in nuetrel. i tried cleaning all passages venta air filter yes oil level is normal when i first started up it didnt stumble tnen at track it did. wnen i changed spark plug it went away tnen started doing again. yes i tried lowering pilot jet 45 to 42 to 40. it puffed and stumbled at all settings. plot fel screw did not change symtoms. the mid to toprun reak good just in o to1/4 throttle opening.next step replace accel pump diaphram.any ideas? p.s. should the bk mod be done on 2002 model this is a canadian model.spes 150 main 42 pilot 1&3/4 fuel screw.