hey i was on here a couple of months ago having problems with my xr3i not reving past 4200 but its now sorted thanks to you guys and an american hotrod forum !! it turns out the problem was valve float ! the valve springs under full load were only giving 115 psi but they should of been 160-190 psi !!! so i have made some shims to go under the valve spring seats and its compressed the spring enough to give 172 psi ! result ! now im producing 123 bhp with only a piper cam and a good tune !