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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3976
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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My 1986 9.9 2 stroke is only running on one cylinder the top

Customer Question

my 1986 9.9 2 stroke is only running on one cylinder the top one, replaced plugs and plug wires, no help, switched solenoid bottom cyl still did not fire but top on continued to fire with switched solenoid
Submitted: 2 years ago.
Category: Boat
Expert:  Charles replied 2 years ago.

Hello, my name is***** will assist you today.

Is the motor a 86 or a 96?

Would you please post the serial number of the engine?

Customer: replied 2 years ago.
Customer: replied 2 years ago.
trigger asssembly was also replaced
Expert:  Charles replied 2 years ago.

1986, thanks.

The first thing that you will want to do is a compression test. Make sure tht both cylinders ore over 90 PSI. If not, the engine will not run good at all. After that, if the bottom plug is cleaner, white, than the top plug, you have water getting into the cylinder. There are two places that this can happen, the exhaust plate or the powerhead gasket. Stat by replacing the exhaust plate gaskets, try the engine. If it is still doing the same thing, replace the powerhead gasket.

If you have any questions, please let me know.

Customer: replied 2 years ago.
Okay, I will check these. I have also put a spark plug tester on both wires and there is no spark from the coil to the bottom cylinder plug. Will the poor compression or water in the cylinder prevent the coil from sending a spark to the cylinder?
Expert:  Charles replied 2 years ago.

No, if you do not have spark and you have already replaced the stator and the trigger, the switchbox is bad.