got the top end of my 86 xr6r. i'am waiting for a reply on a few questions from barnums, if all is good i will be going to a 628 and a stage one or so cam, new valve springs and new ceramic coated oem head pipe(ordered) i will rebuild the carbs, re-jet (already 5 sizes larger than stock) and it could go more. i think i will be pulling a pretty large amount of fuel air mixture. i have never had a prob. w/ the dual carbs so i'am going to get as much as i can from them. i will be sending the top end to barnums so that will be good. this thing should friggin haul. look out 650r's.