What precent fuel are you running ? and why may i ask are you swinging a 17x6 APC? try a 15x8 APC! thats what I run on all my YS's also found that they run best on a McCoy plug. I would start at the high end needle about 2 turns out and and maybe 1 to 1 & a half on the low end. and go from there, sounds like it may have some dirt in there also. I've noticed when i buy a new YS they always seem to have just a little tiny piece of dirt somewhere