Merc 150 problems...

[nscvol]

Hey guys. I have a 1980 Merc 150. Engine runs great when on the muffs. put it in gear and it revs quickly. The problem is when I put the boat in the water it will not rev up or accelerate. It feels like it's dragging a 1000lb anchor. The engine is not missing or cutting out in any way. it just will not rev and pull like it should. The top speed is maybe 8mph. The plugs are new, fresh gas and oil.. New fuel line and filter. Everything is OK as far as I can tell. I have been told by a few people that it sounds like the coils are bad or weak. Does this sound right?? Any help would be appreciated..

 

[TightlineT]

Mr. Wrechin2 will be able to help you out. He's saved a bunch of us on here!!! emoCool

 

[wrechin2]

The most common thing would be a stator or a switch box. Very rarely will you see a bad coil. The stator has a transition voltage at 2500-3000 rpm's. Switch boxes will usually drop 1 or 2 cylinders. Yes, it will run good on 5 cylinders on the hose but run like dog do-do in the water.

If you have acess to a timing light, while it is running on hose, verify that all 6 are firing. If not, then post what you found and I can walk you through some more "home test" on it.

Where are you located at???

 

[nscvol]

Thanks for the reply. I have a timing light but am unsure how to check the timing... I live in Chattanooga.. Thanks again Wrench!

 

[wrechin2]

What I need you to do is connect the timing light onto each spark plug wire and simply see if it flashes. Hook the timing light to the battery and then to each cylinder and note what the timing light is doing. If it flashes there is spark going through the wire but doesn't indicate how strong. If it doesn't flash, this indicates no spark going through the wire. This is a simple way to see if all are firing. With this type of ignition, you can have a couple of dead cylinders and it will still run under a "no load" situation. Hope this helps!

 

[nscvol]

OK.. Did all that. All of the cylinders are firing. Any ideas now? Thanks again Wrench!

 

[wrechin2]

Now a lake test! Take the timing light and cable tie or tape the trigger to the "on" position. This way you can lay the timing light on the deck and watch it without holding it. Put it on each of the cylinders again and see if they all continue to "FLASH" when it acts up. If you are getting around 2500 to 3000 RPM's it is more than likely a stator. Most commonly it will drop all cylinders on 1 side of the engine at these rpm's. Let me know what you find!!! We are trying to rule out ignition for the most part.

When did it start this???

 

[nscvol]

Actually it has done this since I have owned the boat. I bought the boat "as-is" but it started up just fine. We took it to the lake with high hopes and the think ran like poo. I drained the fuel tank, put in fresh gas/oil, new plugs, checked the fuel filter, and the carbs. Took it back out and it was the same thing... I brought it back home and parked it. Now I'm trying to fix it and having a tough time with it. I really appreciate all your help!


Also, the tach doesn't work.. I haven't experimented with it much, but the wiring might not be hooked up right on it. I have read that the:

Purple is the 12V from the switch
Black is the ground
Gray is the tach input
Brown/white goes to the "S" terminal on the trim gauge
And the Tan is the Warning Horn

Does this sound correct?

 

[wrechin2]

No problem! If this test checks out good, then there are some test that will require 2 people to test it. Hopefully it turns out to be something simple.

emoToast emoToast emoToast

 

[Oldman]

nothing simple about a boat.lol

 

[nscvol]

Also, the tach doesn't work.. I haven't experimented with it much, but the wiring might not be hooked up right on it. I have read that the:

Purple is the 12V from the switch
Black is the ground
Gray is the tach input
Brown/white goes to the "S" terminal on the trim gauge
And the Tan is the Warning Horn

Does this sound correct?

 

[wrechin2]

That is it!!