1989 Honda Accord misfires when driving
I have a 1989 Honda Accord LX carb engine with 199,300 miles on it. It misfires or jerks when accelerating or when engine is under load. Not continuously, but enough to be annoying. Changed plugs, wire, coil, dist cap and roto with no luck. I did have timing belt changed last year. Problem started about that time but unsure about that. Asked same mechanic if anything done with the timing belt could cause problem and he said no. He has checked timing again and ran a scope on engine. I changed plugs twice thinking maybe I got a bad plug. When doing so, I noticed that # 4 plug had residue on plug when others did not. Not any oil substance, just loose dry matter that probably came from unburnt fuel. Drove vehicle several months and checked plug again and same plug dirty with residue. Had vehicle back to same mechanic this morning and he said he thinks it is the distributor, but that I should just continue to drive it until it could be verified better. What do you think?