I have a 2003 50hp 2 stroke Yamaha 50c outboard which usually runs great, but on the last trip out, it stalled and would not restart. It turns over and runs for a few seconds, but then stalls out again. Plenty of fuel in the tank, and there is a new fuel/water separator.
I noticed air in the oil line so I thought maybe oil wasn't getting to the cylinders. I figured maybe this would cause a loss of compression and might cause it to stall. So I checked compression and got 70, 70, 80. I shot TCW3 oil into each cylinder and turned it over a few times, then checked compression again. This time I got approx. 115 in each cylinder.
I figured I'd try to start it again and it ran perfectly (except for the obvious white smoke pouring out of the motor because of all the oil I had shot in there). But then after about 30 seconds of running well, the engine dropped to idle speed (which is normal), but then stalled out. I'm wondering if this could be because it had burned off all of the oil in the cylinders and was now back to having low compression again. I am thinking that it's the oil pump that may have failed, but I don't really know. I know that most people would say that the head gasket failed, or it's the rings or pistons that have issues, but I really don't think that's it. Like I said, the boat ran well that day, and it is well maintained. I'm thinking the problem is more along the lines of a gas or oil issue rather than major mechanical malfunction. I should note that the time it ran great was its first run after being stored for the winter. I started it right up and it worked fine until about an hour later. All last season it ran great with no issues. I'm worried that I may not have used enough fogging oil when I winterized it. I sprayed it in until it stalled, but I don't remember putting any into the spark plug holes directly. I wonder if I didn't coat it well enough and may have caused some rust inside the cylinders, or something along those lines. Not sure where to turn next. I know the motor runs great when I shoot oil into it, so that rules out bad gas, bad spark, bad compression, etc. But how do I keep that compression up? Could it be as simple as a faulty oil pump? Like I said, there is a part of the oil line that has air in it (about an inch long), so oil may not be reaching the cylinders. Could that cause low compression and stalling? Thanks in advance, I greatly appreciate any help!
I noticed air in the oil line so I thought maybe oil wasn't getting to the cylinders. I figured maybe this would cause a loss of compression and might cause it to stall. So I checked compression and got 70, 70, 80. I shot TCW3 oil into each cylinder and turned it over a few times, then checked compression again. This time I got approx. 115 in each cylinder.
I figured I'd try to start it again and it ran perfectly (except for the obvious white smoke pouring out of the motor because of all the oil I had shot in there). But then after about 30 seconds of running well, the engine dropped to idle speed (which is normal), but then stalled out. I'm wondering if this could be because it had burned off all of the oil in the cylinders and was now back to having low compression again. I am thinking that it's the oil pump that may have failed, but I don't really know. I know that most people would say that the head gasket failed, or it's the rings or pistons that have issues, but I really don't think that's it. Like I said, the boat ran well that day, and it is well maintained. I'm thinking the problem is more along the lines of a gas or oil issue rather than major mechanical malfunction. I should note that the time it ran great was its first run after being stored for the winter. I started it right up and it worked fine until about an hour later. All last season it ran great with no issues. I'm worried that I may not have used enough fogging oil when I winterized it. I sprayed it in until it stalled, but I don't remember putting any into the spark plug holes directly. I wonder if I didn't coat it well enough and may have caused some rust inside the cylinders, or something along those lines. Not sure where to turn next. I know the motor runs great when I shoot oil into it, so that rules out bad gas, bad spark, bad compression, etc. But how do I keep that compression up? Could it be as simple as a faulty oil pump? Like I said, there is a part of the oil line that has air in it (about an inch long), so oil may not be reaching the cylinders. Could that cause low compression and stalling? Thanks in advance, I greatly appreciate any help!