Outboard Problem

[Iambjm]

I have a 2003 25hp Merc 2 stroke, I recently had a problem with it not wanting to run when I turn the throttle up, and when I did get it up to full throttle it ran at about half the power. Took it in to a marine dealer, they changed the plugs and tweaked the carburetor and said t was running on only one cylinder and they didn't know why. Got it back and it ran great for about 2 weeks, I was running around the lake to charge up the battery and it seemed like it misfired a couple of times. Next night I went out fishing, and bingo back to the same old problem. Any ideas where to look for the problem before I haul it back into a boat dealer?

[sunniewally]

had a bad coil on mine when it did that. find out which cyl it is.

[boatfixer]

Spark, fuel and compression

That being said, id want to determine which one is absent.

Switch boxes (CDI box) are known to fail.

Fuel filters plug etc.

If the dealer had no idea why it was only running one 1 cylinder, find another shop. Pretty basic engine and it shouldn't be hard to figure out

[MNHunter65]

I recently had a very similar problem with my Mercury Optimax. I tried plugs and a new fuel filter before bringing it in. Turned out to be a bad coil. Runs good now.