08-05-15, 05:20 PM
Back fires would indicate un burnt fuel getting into the exhaust, ie some sort of spark plug misfire. if you changed the plugs you would obviously have had to pull off the plug caps, check that the ht leads are still tight in the caps, and just as a long shot, did you spray anything into/over the plug caps before refitting ? there are many products out there ie brake cleaner which leaves a conductive surface when it drys. perfect for causing misfires and back fires . The only safe product I've personnally found is WD40,
Old enough to know better