Re: Low compression in bottom cylinder

[shane-r13]

quote zul8tr:

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.

Top compression to high? Is that such a thing? I’m hoping its carbon. I ordered some cleaner and am waiting for it to arrive.
To perform the test it was cold, wide open throttle. I literally pulled it from storage put it in a barrel and tested it. I think maybe thats where it went wrong, maybe carbon or stuck ring etc, form sitting and since i didn’t run it to MAYBE free it up. Anyways i’ll run the cleaner through it when i can and report back what happens.
As for oil, I usually use just a shell brand outboard oil or mystic outboard synthetic. Honestly i’m not highly picky on oil, while i should likely be, as with the little use the motors get a year. And for gas, I have never found a reliable source that is E free in my area. I think i can buy it in 104 Octance at the race track and its E free haha. Seems like no matter the company or grade its there. A little birdy once said you basically cant get it E free in Canada but who knows.