25hp Mariner problem

I have never had a problem until now. Went to my fishing spot at WOT, backed off the throttle to hit my spot on the GPS. Just before idle it began to run rough. Now it only fires on one cylinder and is very weak. I have trolled with this motor for extended periods of time and when it was time to head for shore, it would be firing on one cylinder for about a boat length and starting to raise the bow before the second cylinder fired. Now it will barely make a wake. I did a visual and didn't see anything obvious. Pulled the plugs and found great spark on both plugs (be careful where you put your hands during this test, it bites. Ask me how I know). This limited info may not be of much use but I thought I would through it out there.

Thanks
HANGEYE

ps The motor is a 1998 model.

First thing to do is a compression test. If you don’t have a tester, I’d buy 2 brand new spark plugs first. If that doesn’t fix it, get a compression tester and eliminate that. That gives you something to do while you wait for Pappy to show up on this thread.


Sent from my iPhone using Tapatalk

Thanks for the reply Weldor. Replacing the plugs and a compression test is something I should have tried right away, but I haven't worked on any kind of motor in years and I'm getting old and the memory just doesn't work like it used to. On my way to get some spark plugs. I'll let you know what I find.

HANGEYE

Pappy & weldor. Thank you very much for sending me down the correct path. Called my son for some much needed help. Together we flushed the fuel system and replaced old gas with new (old gas went in my truck, about 3 gal.). My son pulled the carb and gave it a good cleaning. While he was doing that I replaced the impeller (water pump). Put everything back together and fired it up. Runs perfect. Oh ya, the compression test showed 130 on top and 129 on bottom, our "guess" is that should be good. Thanks to you gentlemen, it looks like i'm going fishing this friday after all. Thanks again fellas.

TIN BOATS IS THE BEST

HANGEYE

Very little wear on the internals of that motor. You're getting about 9:1 compression, which is towards the upper limits of what 87 octane is safe for without knock sensors & electronic timing adjustment.