I have a MerCruiser 3.0 with est ignition. I'm getting backfiring thru the carb @ 3000+ rpm. I'm seeing sparking between timing tab and pulley. I replaced the coil, new cap, plugs, wires, rotor, last year. Got any ideas?
The sparking you are seeing is static electricity. I was at a Mercruiser service school and someone noticed the sparking and the instructor explained the belt has nylon or something similar which charges the crank pulley, since the pulley is insulated from the crankshaft section and the tab is close enough for the charge to jump. It would be really weird if the static discharge is causing the mis-fire.
THANKS GUYS FOR THE INFO! I was trying to locate what was happening because my engine was misfiring and noticed this sparking happened at the same RPM that the engine was misfiring. So they are actually not connected! Tonight I went down to observe my engine running at night. What I observed was sparking coming out of the spark plug boot on cylinder 1. These are one year old plugs Sierra Blue wires. Do they need to be replaced?
Could be the cap, wire or plug. If the plug or wire has high resistance, there can be arcing. If the cap has a carbon trail, there can be arcing. Try cleaning the cap with brake cleaner and a wire wool or scotch brite. Then blame wire and plug.
Also, make sure that both ends of the plug wire are firmly connected to cap and plug.
