Hi, i own a 1992 fxlr which has developed a misfire, i think its on the rear cylinder. i put 2 new Ngk r DCPR8E plugs in and it ran great. left it a few days went for a short ride and it began misfiring again and back firing through the exhaust. i changed the plugs again for used ones but it still seemed to run on one cylinder.the bike has had a twin coil conversion, a crane programmable electronic ignition module (Model Hi 4) and a Mikuni 45mm carb,a 96cu and 1600cc conversion. the bikes only done 9000miles .And it has a new battery. can anyone Help? and also recommend any other spark plugs that might be better? thanks for all help received. Dave.