I have an XT and walbro 990 carb with CPI pipe. engine ran fine for a couple of tanks after pipe was put on, then started to really bog until about 3/4 of full RPM then takes off like a banshee. I have tuned it every way possible and nothing will change it. Another guy I know is sending his straight to Redcat and they are going to look at it, cause they say it shouldn't run like that. My question is does anyone out there have any idea why??? Is it a seal leak? Please no tuning responses. I have done everything to it, changed head and piston and rings, different carb. Nothing changes it. HELP!