MRichardson
Well-known member
I have 94 Merc 25hp 2-stroke that I've been running for about a year and a half. Last year, compression numbers were "real good" according to my mechanic. Don't recall what he said they were though.
Last weekend while out on the water, it started fine, idled fine, etc. but would not accelerate or rev beyond 25% or so when I opened the throttle. I checked the linkage, etc. to be sure the throttle was in fact opening up, and it was. I got it hope, checked the sparks and the plugs themselves, no issues. The motor would rev with no load (out of the water).
I borrowed a compression tester and got 60 & 60 on both cylinders. This is ridiculously bad compared to the performance I was getting, and results from a year ago or so. Hard to believe it good go that far south in such a short time without doing something drastic like not putting oil in the fuel. I do, btw, and in the right ratio.
Since both cylinders are bad, I'm assuming it has to be something affecting them both. I pulled the cylinder head cover on this motor, but the one on the back just covers the tops of the cylinders. Can't see inside other than through the spark plug holes. It's really the cover for the reservoir the water flows through on the way out for cooling. I don't see how this could affect the compression inside the cylinders. Trying to find if there's another gasket deep down in there. Since it's both cylinders at the same time, decreasing by the same amount, I doubt that it's piston rings, pitting/scarring on cylinders walls, etc.
Which brings me back to questioning the comp test to begin with.
Last weekend while out on the water, it started fine, idled fine, etc. but would not accelerate or rev beyond 25% or so when I opened the throttle. I checked the linkage, etc. to be sure the throttle was in fact opening up, and it was. I got it hope, checked the sparks and the plugs themselves, no issues. The motor would rev with no load (out of the water).
I borrowed a compression tester and got 60 & 60 on both cylinders. This is ridiculously bad compared to the performance I was getting, and results from a year ago or so. Hard to believe it good go that far south in such a short time without doing something drastic like not putting oil in the fuel. I do, btw, and in the right ratio.
Since both cylinders are bad, I'm assuming it has to be something affecting them both. I pulled the cylinder head cover on this motor, but the one on the back just covers the tops of the cylinders. Can't see inside other than through the spark plug holes. It's really the cover for the reservoir the water flows through on the way out for cooling. I don't see how this could affect the compression inside the cylinders. Trying to find if there's another gasket deep down in there. Since it's both cylinders at the same time, decreasing by the same amount, I doubt that it's piston rings, pitting/scarring on cylinders walls, etc.
Which brings me back to questioning the comp test to begin with.