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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3311
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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Dominick, I have a 1992 70hp. I had to replace the top

Customer Question

I have a 1992 Johnson 70hp. I had to replace the top piston last week as it was damaged. I noticed this after it felt like the boat was running at less than full power on the water. Compression test revealed zero on the top cylinder. So, as stated above, I replaced the top piston. Now, I cannot get the motor to start. I have compression, spark and good fuel. It cranks, but will not start.
Submitted: 3 months ago.
Category: Boat
Expert:  Charles replied 3 months ago.

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

You are going to need to verify that the timing on the engine is correct now that you have it back together. And also run a compression test. You need over 80 PSI each just to get it to run. Over 90-100 is where it should be to run correctly. Also run a spark output test on a spark test tool.

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