98'wr400, appears to have a misfire on 3/4 upwards throttle, only been out 3 times and its my first 4 stroke any obvious causes, not sure of any specs of the bike. Done the usual and cleaned carb, filter, new plug fresh fuel but its still the same. Bought it without airbox lid so fitted one and it wouldnt run at all, removed it and its back to misfire on 3/4 throttle. Read other post re over oiling the filter, will clean and reoil but what else???