I had a similar problem when i finished my serval build. It ran good on the bottom but fell on its face just as it was getting on the pipe. I chased it for a while checking boots, wires, coil, gap clearance, fuel / carb issues, jetting, everything. I jetted from 160 down (28pwk's). I got to 125's and it was still rich. I knew this couldn't be right. I thought that it was only running on one cylinder bc one pipe was much warmer than the other. I dont have the money for shearers yet so i threw on a set of t5,'s with a spark arrestor / hush kit that i had laying around. I knew they would be restrictive but this was rediculous. I was stumped and began to think something had plugged up the stingers. I took them apart but they were clean. When I was putting them back on I decided to look at the spark arrestor. The screen was completely plugged. I have never really ran a spark arrestor before so it hadn't even crossed my mind. I pulled the screen out and cleaned it real good. Problem solved. I know its not likely that the exhaust plugged up while you were riding but thought that I would throw it out there. Sorry for writing a book but I wish I could have found a post like this so I hope its helpful to someone. Bottom line, as with everything, start basic and work your way through. I would start at the plugs and work my way through the electrical system. I know you switch plug wires which likely eliminates them but I would recommend you call Jeff at fast and get some of the taylor wires just to be sure. Cheap upgrade and so far seem to be a solid product with a really secure fit. Jeff told me that he ran them on his drag bike for a long time until he upgraded his coil. It also could be the coil breaking down aon the top end or when it gets hot. Anyway I hope you get it all worked out...