Mercury 150hp 2002 jerking/running rough at random times

jaza2003

Cadet
Joined
Feb 10, 2017
Messages
8
Hey guys,

I am a newbie when it comes to boat only recently buying one.

The boat has been running great with only some minor issues.

The boat at one stage began jerking at random times, it wasn't consistent, as in it may jerk for 15 minutes then not jerk for the rest of the day. Then it might jerk for half hour then again not for the rest of the day. I decided to change the spark plugs first and it seemed to work, the boat ran great with no jerking whatsoever. I then did the water pump with a mate, and they temperature of the boat improved, all was good.

the issue now, is that the jerking has began again, but along with that the boat is now sluggish. Then it will come good, and will be fine. Today was the same, would run sluggish, come good, then jerk and became sluggish again but remained that way for a while. I put the ears on to clean her when we got home and it was running rough, really rough. Still starts first crank, but sounds rough with a mild popping sound.

My first theory is fuel, my reason for this is when I did change the spark plugs I was at another location using fuel from a different station, and whilst there it ran fine. As soon as I got back and used fuel from the local servo it would jerk for a little at times and then come good and repeat.

I hope that was convoluted, but I am not sure what it could be? I am planning on buying a new plastic fuel can tomorrow and hook that up with fuel from a different place, because the tank I have on board is made out of like tin or something.

Thought i'd also add, when Im going full throttle it doesn't jerk or seem sluggish, only feels like its not reaching top speed.

Any questions to clarify ask, cause I don't know if I made sense even after reading it back to myself.

Thanks
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,454
Use a timing light to trouble shoot this.-----------Hook it up to plug # 1 and run on the lake.--------Observe behaviour of spark.--------------Repeat the test on the others.
 

jaza2003

Cadet
Joined
Feb 10, 2017
Messages
8
I'm really not sure how to do that racerone!

I took it out today with some gas from a different station in a new tank.

It was less sluggish but is jerking at low speeds, once I open her up the jerking is gone..

Any solutions what it could be?
 

jaza2003

Cadet
Joined
Feb 10, 2017
Messages
8
Ok, so I should have done this before posting, I feel stupid.

I took the spark plugs out and cleaned them up, they had wet oil on them and looked fouled... the plugs cost like $27 where I'm from so getting new ones right now wasn't an option. I cleaned them up, and then took her out and all the jerking and stuff was gone... it sounded great and felt like I had power back.

Now my question is, what is causing the plugs to foul? I recently run out of oil in the reserve and the alarm was sounding but I topped the reserve up and they alarm is gone and the unit on the engine remain full.is it possible I have done something wrong when filling the reserve etc?

Thanks guys for all the help
 
Top