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Mercury 800 Thunderbolt Misfire

H

Headstash2

New member
I have a Mercury 80p Thunderbolt with a missfire. I have changed the plugs and slightly scuffed the distributor cap contacts. Still sounds like its running on 3 cylinders. What should I be looking at or just try and find a new cap and wires. Not sure if wires and cap are integrated or can the wires be removed. Tried unthreading the wires but they wont budge. Where would I find parts for this motor. The serial number plate # is 3058091. Not sure if a 9 is the first number. Also looking for prop and gearshaft seals. Please help want to go fishing but dont want to hurt the motor.
 
If the number is 3058091,it's '71. If it's 9058091,it's '72 Belgian built Mercury.It will depend on your location. No difference in the engines.
Run it in the dark,there may be a spark leak or short somewhere.
The wires can be removed,they unscrew.Check the spring loaded carbon brush in the middle of the distributor cap.Look for cracks.
If you can get the HT leads out check them for continuity,then heat them and check again.If they are the original,I would replace them anyway.
Good luck,I have one myself,'69,and I think they are practically bulletproof,link to parts http://www.marineengine.com/parts/mercury-outboard-parts/800-4-cyl-80-4-cyl/2559001-thru-3493912
 
Miss fires on these motors can be ignition related(see above) or mechanical due to lower seals weeping water into cylinder,warped exhaust divider. Inspect the plugs for water dropplets or rust. What is compression?
 
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