The bike was rejetted with the k&n mod but not the qseries pipe. I am not sure what size jets since I had the dealer rejet it last time. (that will teach me) The plug is perfect, medium brown in the center. I ride at around 4500ft elevation. The bike has always had a sputter when backing off the throttle slightly. I have rode it with the mods 6-8 times with no problem. It would climb like you know what... Now all of a sudden, it does not want to climb, but runs good (slight sputter) up and down the street. I am going to pull the carb tomorrow to see what jets are in it.
I have a 2001 xr400, qseries pipe, k&n air filter. The bike runs pretty good on the flats, slight hickup when not on the throttle, screw the throttle on and she goes... Problem is when climbing hills, acts like the choke is on. What gives???