I have a 1991 Mercury Black Max 150 that is driving me crazy.
Serial: 0d021340
Model: 1150412LD
This past spring it got where it was running bad and I began diagnosing my problem. I narrowed it down to a bad stator and replaced the stator. It ran good after that, but it did seem to not quite have the full power it normally had and at top speed it would occasionally seem to slightly surge between running at top speed as it should to seeming like it was not quite reaching its full power.
It began getting worse and finally got where it would crank up and run as it should and would rev up, however when you gave it gas to take off it would only reach a trolling speed and will stay at that speed with the throttle wide open or would just bog out and turn off.
Here is the what I have diagnosed to try and solve this problem.
The first problem I noticed was the fuel filter seemed to be darker than it should be. Took it off and cut it open to find black pieces of fuel line all in it. I replaced the filter and all the gas lines and the primer bulb. I thought that would fix it, but when I put it out to try it, it cranked right up and idled, but still would not go faster than a trolling speed.
I then checked the compression and I am getting around 110 on all cylinders.
I checked the fire. Fire looked good on all cylinders. I have recently tested it using a spark tester set at 1/4" and it is getting good spark on all cylinders.
I then pulled the carbs. I saw nothing in them that looked to be a problem, but I cleaned them, replaced the gaskets and put them back on. This made no difference in the problem.
I pulled the fuel pump. Took it apart and saw no noticeable problem, but I still picked up a kit and rebuilt it. This made no difference.
It does seem to be hard to start at first, but after it starts once, it cranks right up each time afterward. I seem to detect a slight miss at idle, but otherwise it idles fine though it does seem to idle a little slower than it should.
So, what should I check next? All I can think is I may have a trigger assembly or switchbox that goes out under load, but I hate to just start throwing expensive parts at it without a way to know for sure. Also, I guess this could be a fuel related problem, but I am not sure how to diagnose that either?
Thanks for any help anyone could give.