I've been having an intermittent problem with my 2-stroke Merc 15 for a couple of years now. In the past it's occurred pretty rarely (once or twice a season) but has been happening more frequently this year. I've had it into the shop three times now and they seem to have just about run out of ideas. Would sure appreciate it if anyone here has a thought.
Here's what happens:
Motor starts fine and runs perfectly for a while (anywhere from 20-40 minutes) and then at normal running speed (say 3/4 throttle) it loses power. It doesn't die - it gradually slows down and you're left running just above trolling speed. Stop the engine and it will restart immediately, but the problem continues. Give it more than about 3/4 throttle while this is going on, and it will die (but will restart right away).
It will run like this for 15-20 minutes, then it'll cough and suddenly pick up and be back to normal - but only for a short while before losing power again. One time while I was stuck out there with it running this way I pulled the cowl off and looked into the carb - didn't look like much fuel was coming out of the jet. Then when it regained power you could see the fuel spraying out again. Squeezing the primer bulb doesn't make any difference.
A further wrinkle is that I've noticed that when it's lost power, I can get it to start running right more quickly by taking the cowl off and leaving it off. The hotter the day the sooner the problem seems to crop up, so I'm puzzled by whether it's really a fuel starvation issue or some kind of overheating issue.
So far the shop has cleaned and inspected the carb and fuel filter, replaced a torn bleed hose and fixed a loose ignition wire, but they've been unable to replicate the problem so they're just going on my description of it. I've run the motor using two different hoses (one brand new)and two different tanks, but regardless, if I drive around long enough this happens.
Before I take the motor back for a fourth shop visit I'd like to solicit some other opinions. Any help appreciated. Cheers!
The damn things never want to act up when there is a mechanic around, you need to take it to a service shop with a test tank where it can be run till it acts up, anyway it does sound like fuel, we had one that acted were much like your problem and after many hours of cussing at it it turned out to be the high speed winding in the stator and it would not even show up with a DVA, I talked to a mechanic from CDI electronics and he said change it, so we did and it's still running
Thanks for the reply and the idea! The shop I've been taking it to is a big Merc dealer and they've been running it each time without being able to duplicate the problem. The last time, they ran it for an hour at WOT and at that point it started to run intermittently on one cylinder. Tightened an ignition wire, then ran it WOT for two hours straight and said it ran fine. I got it back, took it out and it only took me half an hour to get it to lose power again.
They weren't using my tank and line, but since I've changed tanks AND lines and still have the problem I don't think that's it. The last time I was out with it I noticed that the loss of power happened exactly at the moment I was throttling down, after having run at a constant speed for a few minutes. Instead of slowing down slightly as I intended it slowed right down and stayed there. If it has something to do with opening and closing the throttle, running it in a tank at WOT might not make it show up anyway.
Sure seems like a fuel starvation issue but no one can find any evidence of that so far. Since it seems to run better w/o the cowl and in cooler weather, could it be a thermostat thinking it's overheating and then limiting power, like S.L.O.W. on an OMC?
If not, then something is stopping the fuel from getting to the carb, but only sometimes and only when the motor is good and hot.
Did you ever solve your problem? I have a 96 Force that performs similiar to your motor. I found a bad spark plug-the electrode was broken. The engine seems to run fine at idle and low speed, but it won't power up when you push the throttle above the halfway point.
I've read a lot of post's on this topic and it seems like it has to be either a problem with the stator or the something in the drive system.
CDI website has a troubleshooting guide for checking out the stator. I think that is the easiest thing to check out first.
Yes, I did finally trace it to an ignition problem where it starts running on one cylinder when it gets hot. Snugging up the #1 cylinder spark plug wire seems to solve the problem temporarily, but it eventually comes back. The tech at the shop was thinking it could be a coil or even the power pack. This is a basic manual start motor.
Thanks for the suggestions. Some more investigation is needed but it was good to be able to narrow things down and eliminate fuel as the problem.
2000 Mercury 15 power loss
Linear Mode
