Hi, Have aquired a 1991 TT250 with unknown background. Was running poorly and found inlet manifolds (dual throat carby) badly cracked and carby full of GRAVEL (dont know how it was running at all). Have replaced the manifolds and quick clean of the carb and symptoms now are: starts quite easily and idles quite nicely all the time and seems to run quite well when stone cold, but quickly develops a significant mid-range misfire. Full throttle seems to overcome misfire region but its a bit hard to ride flat-out ALL the time. Sometimes misfires and stalls at low revs too. Valve clearance seems to be a bit tight (about .05mm in and .08mm out) and requires shims to adjust. Spark plug is new but is running fairly sooty. Any thoughts if the misfire could be due to valve clearance, fuel or electrical?? and/or any easy way to check (if there is such a thing) would be appreciated.