Re: Low compression in bottom cylinder

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Pete

US Member - 2 Years
Replies: 154
Topics: 6
#74724

Maybe the top is bit too high and the bottom a little low from carbon? Run the engine with the cleaner suggested and retest. Did you do the test cold with throttle full open? I do them cold that way so temp is about the same for test and not influencing results. Relative consistent results matter a lot and conditions should be consistent from test to test. Take a peek in the spark plug holes with a flash light and at least observe the top of the pistons and see if there is a lot of carbon rotate crank to put piston at bottom of stroke for a better view.

What oil are you using? If Mercury Premium Plus it has a lot of Moly Di sulfide and is a dirty oil with lots of build up, especially if you go slow a lot. I use to use it and had to add Mercury Quickleen #2 each fill up to the fuel to keep the carbon down. BTW 40:1 is not that rich since 50:1 is the usual mix.

https://www.mercurymarine.com/en/us/par … -products/

Although I have never used it the Mercury Powertune looks like a good start. Why don’t they list it on the Mercury Marine site?

Are you using E free fuel? You should be.