Mercury 40hp 2000 3 cylinder, not getting over 3000 RPM's?

[Chris Cole]

Hello forum,

I am new to this forum, I have been reading threads to try to fix my motor. I haven't had any luck yet. I hope someone can help me? Here goes.
The problem started after I ran my motor hot. My thermostat got clogged with duck weed. It wouldn't allow water to circulate. I knew my motor wasn't peeing, but ran my motor anyway. After this experience I can't seem to go above about 3000 RPM's, sounds like Iam running on two cylinders. Also, sometimes the motor Idle's well, other times it runs real rough, I have to rev it just to keep it running. As a result of running my motor hot my thermostat melted. I replaced the thermostat, but that hasn't fixed the problem. I have checked the compression in my cylinders after the incident. The readings I got were right about 100 (Cold) in all three cylinders, so that is not the problem. I also had a leaky fuel line connector, that I thought would cause the WOT problem, I changed the fuel line connector; no change, still 3000 RPM's. I put new spark plugs in and tested the spark last night and found that it was intermitent. It was sparking some times, other times it wasn't. When I put a timing light on it, the light would blink sometimes, and other times it wouldn't.
REV LIMITER:I tried disconnecting the rev limiter (Black/Yellow Wire)? I also disconnected all wires from the rev limiter and the motor still ran, is this right? ( I have four wires coming out of the rev limiter, Black/Yellow which connects into two black yellow wires. Purple, which connects into another purple that is not being used. Brown, which connects into two Browns. Black, which is for ground.
Trigger: I did an Ohm test for the trigger there are four wires coming from the trigger. Purple,White,Brown,Black. I tested resistance across all of these connections and I never got a reading (Nada). Today I ran the motor a little bit with ear muffs, and after having run the motor I tested the trigger. I had 10 or 11 MegaOhms from Black to Black coming out of the trigger?
Stator: I did an Ohm test for the Stator (600-700 Ohms). 4 Wires coming from the stator. Green/White, which connects into two Green Whites. White/Green, which connects into one White Green. White with Blue Stripe, Which connects into another White with Blue Stripe that is not being used. Black goes to ground. Last night the Ohm test passed with flying colors, this morning I could not get a reading????

There are not too many electrical components on my engine; trigger,stator,coils. I am baffled, should I rip my flywheel off and replace my trigger? I feel like that is a guess. Please Help.

 

[Wilsonriverfisher]

Re: Mercury 40hp 2000 3 cylinder, not getting over 3000 RPM's?

how long did you use it with it not pumping?

 

[Chris Cole]

Re: Mercury 40hp 2000 3 cylinder, not getting over 3000 RPM's?

2 to 3 minutes twice that day.

 

[Wilsonriverfisher]

Re: Mercury 40hp 2000 3 cylinder, not getting over 3000 RPM's?

Wow...Im not a expert but I would recommend taking that situation to the shop. Running the motor without the pump can be devestating and it sounds like you will have a melted impellar as well. Just hope nothing is seroius in the head or combustion chambers. Also if you took off the rev limit and ran the motor the motor wouldnt be able to shut it down when something breaks like getting the cooling passages or thermostat stuck with foreign matter. The rev limit would prevent a motor from being ruined.

 

[Chris Cole]

Re: Mercury 40hp 2000 3 cylinder, not getting over 3000 RPM's?

Motor is peeing okay. I did not take the rev limiter off before the incident. I am going to go check my rectifier this morning. I guess it can't hurt.

 

[Chris Cole]

Re: Mercury 40hp 2000 3 cylinder, not getting over 3000 RPM's?

Recitifier is okay. Can anyone offer any advice? Should I just start replacing electrical components or what?

 

[Jugfisher]

Re: Mercury 40hp 2000 3 cylinder, not getting over 3000 RPM's?

Now I dont know if a power pack is the same as a rectifier ( I dont know all the terminolgy.) That is the exact same problem I was having with mine. The fire was intermittent and I replaced the power pack and it ran fine.

 

[Chris Cole]

Re: Mercury 40hp 2000 3 cylinder, not getting over 3000 RPM's?

Jugfisher,

Do you have the same year and type of motor that I do? The power pack is the rectifier. Maybe my power pack is not okay, maybe someone could help me out with how to test it properly. Here is how I tested it.

B]Power Pack (Recitifier)[[/B]: 6 wires attached to it, 2 Reds, 2 Yellow, 1 black, 1 Grey.
I disconnected all wires from the Rectifier, I then put an OHM meter lead on one of the Red wires going into the Rectifier, I put another lead on one of the yellow wires. I got a huge OHM reading (15 Mohms) like this. I then reversed the position of my leads. My OHM meter kind of blinked strangely, but I don't think it was getting a reading.
My assumption is that the rectifier will amplify the charge one way, but will not allow it the other way due to the diodes contained within the power pack. Is this the right way to check the power pack? Can you help me with this Jugfisher, anyone? Thanks.

 

[Jugfisher]

Re: Mercury 40hp 2000 3 cylinder, not getting over 3000 RPM's?

It sounds like you did all you can do to check it. Now the proper readings of the rectifier i dont know but the way my mechanic and I checked to see if mine was operating properly was it put a spark checker on my plug wires and checked fire. They were firing intermittently so he immediately tried to swap out the power pack. We did and it was firing on all cylinders finally. runnning smooth. He also made the comment that if this didnt wok then all that was left to try was the stator. He had already replaced carbs trigger and piston, and rebored chambers so power pack is all that was left.

No I do not have the same motor as you. I have a 70 hp that is much older. Perhaps this is why my terminololgy is not up to speed. But the big difference b/w the old and new is if you have fuel injection or carbs 2 or 4 stroke. Other than that they are basics are the same.

I ran mine hot and it melted the diodes on the rectifier. Causing it to fire improperly. Its a good guess but not a sure thing.

 

[Jugfisher]

Re: Mercury 40hp 2000 3 cylinder, not getting over 3000 RPM's?

If I can remember and you havent resolved your problem, I will go and test my rectifier and see if i get the same reading as you. I know mine works properly so we will see.

 

[Chris Cole]

Re: Mercury 40hp 2000 3 cylinder, not getting over 3000 RPM's?

Have some breaking news on my motor. First of all the motor ran great yesterday on muffs. Tested the Stator immediately after use. Green/White to White Green 740 Ohms, White/Green to Green/White, 742 Ohms. Stator is okay. Hmmmm????? Tested the trigger. Leave black plugged, test purple to purple,white, brown, 2400 Ohms. Trigger I believe is okay. Hmmmm?????

Looked at my trigger wires going to my CDM modules. The insulation on a couple of the wires that were resting close to the block was burnt, therefore leaving a little bit of exposed wire. I think this might be the problem. I think that the trigger wires are grounding on the block on the way to the CDM, when the motor gets hot.