75 horse merc bogs down at 3000 rpm

[rolmops]

I just acquired a 1984 4 cylinder 75 horse mercury outboard in beautiful condition.It does however have one problem.
It runs like a dream until I accelerate over just about 3000 rpm,at which point it just totally bogs down.when easing up on the gas it comes right back up 3000 rpm.
Should I tear into the carbs or are there other suspects to be considered?
Thanks for any advice.
Rolmops.

 

[emckelvy]

Re: 75 horse merc stalls out at 3000 rpm

Re: 75 horse merc stalls out at 3000 rpm

I wouldn't rule out carbs just yet, but seems to me you're into the main jets pretty good at 3000 rpm. Seems unlikely both carbs would be plugged up in the same manner.

Maybe an issue with fuel pumps or fuel delivery, but the fact that it runs perfectly below 3K then hits the Stone Wall leads me to suspect a bad stator winding.

Easy enough to take resistance readings on the low-speed (blue and blue/wht wires) and hi-speed (red and red/wht wires) charge windings. If they're in spec, you're looking for other problems. Out-of-spec, well there you are!

Here's a handy online resistance chart for ADI motors:

http://www.boatpartstore.com/mercreadings.asp

HTH & let us know what you find.........ed

 

[rolmops]

Re: 75 horse merc bogs down at 3000 rpm

Well I checked the ohmage between the red and the red/white wires and I came up with 136 where it is supposed to be half that much.I also checked while cranking the engine and that gave a zero reading. The stator has been ordered and I hope for the best.
I did order a CDI instead of a Mercury original,everybody I talked to claims that CDI is light years ahead of the mercury electronics.
Thanks for setting me on the right trail.

It gets thicker now.
Just now out of curiosity,I ran the engine up to 6000 rpm on the muffs (for just a split second)
Does that mean that the stator is fine and I should look elsewhere for the source of my troubles?

 

[rolmops]

Re: 75 horse merc bogs down at 3000 rpm

^^^

 

[rolmops]

Re: 75 horse merc bogs down at 3000 rpm

I just got even more disoriented.
In the Seloc manual spec readings It says that for 4 cylinder 75 horse engines between 1984 and 1986 the high side ohm reading between red and red/white is supposed to be between 56 and 76 OHM,but on the specs sheet provided by the boats part store website the numbers are between 125 and 155
ohm.
According to SELOC specs,my 136 OHM is far too high, but according to the boats part store, I am in the money.
Can somebody please hold up a light and lead me out of this labyrinth?

 

[emckelvy]

Re: 75 horse merc bogs down at 3000 rpm

Take a look at this troubleshooting guide from the CDI site:

http://cdielectronics.com/portals/0/downloads/Troubleshooting Guide 2006.pdf

On Page 93 you'll find resistance values for your stator. Where (2) values are listed in (1) block, the top value is for the OEM stator. The bottom value is for the CDI replacement stator.

So, it says for your hi-speed winding, 135-165 ohms, and for a CDI stator, 30-90 ohms.

For the low-speed winding, 5800-7000 ohms; CDI stator is 2200-2400 ohms.

Maybe the Seloc manual is getting these values mixed up. Perhaps someone with specs from a OEM Merc manual can illuminate.

BTW, what values did you come up with for the low-speed windings? If either set, high or low, is out-of-spec, the stator is shot.

And there's tons & tons of great info in that troubleshooting guide.........ed

 

[rolmops]

Re: 75 horse merc bogs down at 3000 rpm

Take a look at this troubleshooting guide from the CDI site:

http://cdielectronics.com/portals/0/downloads/Troubleshooting Guide 2006.pdf

On Page 93 you'll find resistance values for your stator. Where (2) values are listed in (1) block, the top value is for the OEM stator. The bottom value is for the CDI replacement stator.

So, it says for your hi-speed winding, 135-165 ohms, and for a CDI stator, 30-90 ohms.

For the low-speed winding, 5800-7000 ohms; CDI stator is 2200-2400 ohms.

Maybe the Seloc manual is getting these values mixed up. Perhaps someone with specs from a OEM Merc manual can illuminate.

BTW, what values did you come up with for the low-speed windings? If either set, high or low, is out-of-spec, the stator is shot.

And there's tons & tons of great info in that troubleshooting guide.........ed

Thanks for that website.
It is in my bookmarks.I hope to never need it again,but it describes exactly what my problem looks like and it gives the right info in how to solve it.
Great help.Thank you very much

 

[rolmops]

Re: 75 horse merc bogs down at 3000 rpm

I received the CDI stator today and intend to install it tomorrow.
There is one question that keeps on nagging in the back of my mind.
On the muffs,I can rev the engine up to 6000 rpm (I just do it for an instance) but under a load it totally dies the moment I go over 3000 rpm.
Should I pay attention to it not dying at 3000 rpm without a load or is that insignificant as far as stator problems are concerned?