1991 Mercury Black Max 150 - Bogs and will not reach reach high speed

[pamlicopanther]

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.

[leonreno]

Have you done a link n sync on it since the stator install? Timing could be off. Also it may have a factory idle stabalizer that is know to go bad, most of the time they can be removed and it will start and idle better.

[pamlicopanther]

Have you done a link n sync on it since the stator install? Timing could be off. Also it may have a factory idle stabalizer that is know to go bad, most of the time they can be removed and it will start and idle better.

I have not done the link and sync so that would be in order. I just noticed a water leak from the exhaust manifold behind the bracket that holds the coils. I need to pull that and figure out why it is leaking. I hope it is just a gasket. Is it possible water could be getting over to foil a plug due to this? I would think the compression would be low if it was. I have not been able to get it on the water to run it and throttle and check the plugs.

This engine does have a box on the top of the engine that the parts diagram calls an idle stabilizer. Can it just be done away with?

[leonreno]

I believe the box can be done away with BUT you have to reset the timing afterwards and you have to hook up some wires the right way. I don’t know the exact procedure but someone will come along and chime in soon, maybe after the weekend. The leak could be a problem too, definitely get that fixed.

[OnTRAK]

Do you have a Mercury factory service manual (not an aftermarket)? If not, you need to get one in order to do the following procedures correctly. Using the factory service manual. Repair the water leak. Make sure the floats are adjusted correctly in your carbs. Remove the idle stabilizer box and trash it. Make sure there is a bias wire (white-black) connecting the top left lugs on both switch boxes (see wiring diagram in factory service manual). If not make and add one. Do a complete link and sync setting the max spark advance timing to 22*-23* at cranking speed to be on the safe side. Did you replace your fuel lines & bulb with OEM Mercury/Quicksilver and not aftermarket? Aftermarket fuel lines & bulbs have been known to cause problems. Hope this helps!

[pamlicopanther]

[QUOTE=leonreno;11513904]I believe the box can be done away with BUT you have to reset the timing afterwards and you have to hook up some wires the right way. I don’t know the exact procedure but someone will come along and chime in soon, maybe after the weekend. The leak could be a problem too, definitely get that fixed.[/Q

I will check into that.

Thanks for your help.

[pamlicopanther]

Do you have a Mercury factory service manual (not an aftermarket)? If not, you need to get one in order to do the following procedures correctly. Using the factory service manual. Repair the water leak. Make sure the floats are adjusted correctly in your carbs. Remove the idle stabilizer box and trash it. Make sure there is a bias wire (white-black) connecting the top left lugs on both switch boxes (see wiring diagram in factory service manual). If not make and add one. Do a complete link and sync setting the max spark advance timing to 22*-23* at cranking speed to be on the safe side. Did you replace your fuel lines & bulb with OEM Mercury/Quicksilver and not aftermarket? Aftermarket fuel lines & bulbs have been known to cause problems. Hope this helps!

I do have the factory manual.

I have pulled the exhaust plate and have ordered the gaskets I need to replace. I did make a mistake as the leak was from another plate that is sitting on top of the exhaust plate. I believe I could have just replaced that gasket and been good, but it is all apart so I will be replacing them all.

I will check into these other suggestions and see where that leads me.

[JOE54]

better test stator when that happens also loss of spark on one side could be either box or stator

[PartTimeNd]

Did you check to make sure the auto oiler isn't pumping too much oil into the gas? Mine did this same thing and mechanic disconnected auto oiler and now no more bogging out. The reason I'm mentioning this is you said filter was darker than it should be, mine was the same. Mine idled just fine but when rpms raised the oiler would dump too much oil into the mix and it would bog out

[JOE54]

Did you check to make sure the auto oiler isn't pumping too much oil into the gas? Mine did this same thing and mechanic disconnected auto oiler and now no more bogging out. The reason I'm mentioning this is you said filter was darker than it should be, mine was the same. Mine idled just fine but when rpms raised the oiler would dump too much oil into the mix and it would bog out

bad check valves in system