1987 mercury black max 135hp power loss question

[theboatman69]

Hello all,
I have a merc black max V6 135hp outboard. When i first take it out on the lake it runs beautiful and smooth at about 5000 rpm WOT. after about 45 mins, it wont go over about 3000 rpm and starts running rough if I push it, but runs just fine at 3000 rpm. So i got into the forums and started checking the fuel delivery system. I changed my bulb out about a month ago as it was old and flat when i was out on the lake. So it the bulb has been good since. Bulb was hard when i squeezed it but now i don't get that "hard" squeeze when i squeezed it. Seemed like air was in there so i took it off then siphoned the gas back through and its good again. I think it ran pretty low in gas in the gas tank when i was trying to get the old fuel out so maybe it was an airlock? does this sound right? Anyway i decided to take off the spark plugs to have a look. On the port side they are nice and clean but on starboard its another story. All 3 were covered in carbon. I took some contact cleaner and cleaned the plugs and I haven't had a chance to go out to the lake again to try. its had clean fuel since i changed the bulb. I have read a lot about coil and stator problems when this power loss is occurring. What is happening? Is my engine heating up and something electrical is breaking down? Whats with the carbon build up on the one side only? Are we talking switch boxes, coils or stator or maybe everything? I don't really know where to start at the moment and I don't think the fuel delivery has anything to do with it because it was doing the power loss thing even prior to bulb change and when the bulb was good. The guy I bought the boat from suspected there might be a coil issue sometimes when he ran it last year and now this year after winter, it probably did it in you think? Any help is appreciated guys cause when i read the forums about this issue it seems there are mixed things happening to the engine. Maybe the carbon build up on starboard side is and indication or hint of where to start?

 

[Glastron_V210]

I'm new to the 135 game myself, but I did a lot of research before I bought one for my old boat.

It seems these engines are susceptible to stator issues, some of which occur only when the engine is warm. It may also be a switch box (Otherwise known as the CDI ignition unit).

The reasoning behind this is the failure of an entire 3 cylinder bank. Each bank runs from one switch box.


If you have the means, purchase/borrow/make a DVA (Voltage adapter) which allows your voltmeter to measure the stator output easily. Measure the stator output when it's running well, then run it until your poor running occurs, then measure with the DVA to see what's going on.


Chay

 

[Grnbasser]

So when you prime the bulb before starting, does the bulb remain hard. If not, try checking your fuel lines. I have an older black max as well and my fuel lines were old and starting to crack letting air in which was starving the engine of gas. May be worth checking.

 

[theboatman69]

I'm new to the 135 game myself, but I did a lot of research before I bought one for my old boat.

It seems these engines are susceptible to stator issues, some of which occur only when the engine is warm. It may also be a switch box (Otherwise known as the CDI ignition unit).

The reasoning behind this is the failure of an entire 3 cylinder bank. Each bank runs from one switch box.


If you have the means, purchase/borrow/make a DVA (Voltage adapter) which allows your voltmeter to measure the stator output easily. Measure the stator output when it's running well, then run it until your poor running occurs, then measure with the DVA to see what's going on.


Chay

Thank you for your reply. I will get an adapter and try your suggestion for sure. Wouldn't my charging be affected if my stator was bad? I have a real time battery gauge and I can always see that it is charging.

 

[theboatman69]

So when you prime the bulb before starting, does the bulb remain hard. If not, try checking your fuel lines. I have an older black max as well and my fuel lines were old and starting to crack letting air in which was starving the engine of gas. May be worth checking.

Thank you for replying. My gas lines are metal until the hose of the bulb. Could it be my bulb is fubar already??? It worked beautifull before. I will try looking for airleaks at the fittings though.

 

[Glastron_V210]

There are different coils for charging (Low voltage high amperage) and ignition (High voltage low amperage), therefore one set of coils could malfunction while the other work fine.

On the pump ball deal, I just bought a new ball myself and a bit of junk got stuck in one of the one way valves. They are ball-type check valves instead of the old flapper valves on my new one. Anyway, as you might guess, the check valve didn't work and therefore it wasn't pumping gas. I had to disassemble a brand new ball to fix it.


Chay

 

[theboatman69]

There are different coils for charging (Low voltage high amperage) and ignition (High voltage low amperage), therefore one set of coils could malfunction while the other work fine.

On the pump ball deal, I just bought a new ball myself and a bit of junk got stuck in one of the one way valves. They are ball-type check valves instead of the old flapper valves on my new one. Anyway, as you might guess, the check valve didn't work and therefore it wasn't pumping gas. I had to disassemble a brand new ball to fix it.


Chay

I got a "universal" one cause it was about 20 bones cheaper than the oem one. Seemed like good quality. Maybe I'll just spend the cash on a merc one. Is there a good way to check the stator? What am I looking for between leads? I tried forums but they are for different engines. If I change out my stator do I have to set my timing again as well? When I look at the stator for damage what am I looking for? I can't find a bloody service manual for the serial# A932751 anywhere. They are all general or the most common is 0Gxxx xxx and up which I believe is a 92 engine. When I read it some makes sense then it doesn't. Do you think this manual is still around somewhere?

 

[Glastron_V210]

I mentioned the dva. It is how you test the stator. I think at this point you need some professional help to diagnose the issue


Chay

 

[theboatman69]

Lol jumped he gun on asking about the stator again. I'm an electrician by trade so I guess I should be more specific. Got a dva and I will test when it's running good vs when its not. My question is, what is the normal voltage of a good running stator? What leads are best to check between to test if my stator is good and not a weak/faulty coil in the stator? It would be nice to have a benchmark so I could tell if it's on the way out or not.

 

[theboatman69]

Just so I close this thread. Took a chance and ordered a new cdi for the engine because after much reading, and your guys suggestions, I did in fact find that my cdi was the problem. When it got hot, I checked for spark and voltage with the dva when there was power loss. It was so hit and miss. Installed a new cdi, installed new connectors and brushed/cleaned my grounds. Now it runs like a bat out of hell no power loss whatsoever. Thank you guys again for this.