Im not sure if anyone here knows much about boat motors but im gonna ask anyway. Ive got a 1995 johnson 120 v4 2 stroke outboard motor and it intermittently misses once it gets up to temp. things i have figured out; has spark, starts running bad as soon as the thermostats open and it happens everytime, cleaned the carb, i can spray fogging oil in the corresponding carb while its running bad and it doesnt even hesitate. I also pulled the plug wire while its running and it actually makes it run smoother because its not trying to fire on that cylinder, other than that nothing changes when i pull the wire. when i say smoother i mean (while its running bad it poofs and bogs after it poofs then it gets back up to speed and repeats the poof cycle) that cylinder isnt getting used so the miss isnt there, hopefully you cant understand, i do have videos of before and after it warms up just not sure how to put those here. its got great compression, all around 120 +/- 4psi. a buddy of mine told me that it could be clogged fuel lines but im just not sure how that could be a problem only at running temp. the plug is also wet when i pull it out to look at it, maybe its not getting enough fuel? It runs awesome while its warming up, perfect, but as soon as it gets warm and idles down it runs bad, even when i manually give it gas while its running bad it still sounds bad but its just faster. its only one cylinder and its the bottom left cylinder. gotta be honest, if i can figure this out im gonna sell it and get a 4 stroke, these things have problems and they are never a problem that i can figure out. if someone here can point me down the correct path that would make me very happy. for the time being im gonna blow out the fuel lines and im gonna put in an inline filter because it current doesnt have one. (VRO was bypassed so it doesnt have one anymore). oh and ya its mixed gas in the tank. i just want to clarify, while its warming up it sounds perfect, all 4 cylinders. i also havent checked spark after it got up to temp so ill have to try that.
Sounds like an ignition problem. Especially if you said one spark plug was wet. I'd go through that system to find the problem. Check all your plugs for continuity as well with an ohmmeter. It may be something as simple as a bad plug wire. After all, they are 27 years old.
Sounds like a bad spark plug wire and/or maybe that wire is not gripping the plug well and loosening up and you drop that cylinder. Mine come loose sometimes and I'll lose a cylinder until I pull and re-attach the wires.
I have also had strange carb/fuel issues due to water in the fuel, install a Mercury water/fuel separater, every boat should have one particularly if you fill the gas tank using portable gas cans
I have a 2001 Johnson 115HP V6
I see where one would think it’s a plug wire but could that still be the problem if it only occurs once hot?
I could not tell you. Mine seem to come lose with the vibration of the motor, maybe the one boot on yours on just that one cylinder is not holding and it has nothing to do with heat but I'm just guessing