Mercury 90hp 2 stroke has me at ropes end!

[lt4247]

First off there is no Mercury dealer within 50 miles of me so doing work myself to this point.
Driving long distance to a dealer is last resort.

Motor:
2002 Mercury 90hp 3 cyl 2 stroke. Model: 1090412ZN Serial: OT565282.
We bought the motor new and has been used less than 100 hrs. Always ran good with no problems.
Out for first time of season motor ran up fine to 4500 rpm for cruise and after 1 minute it then suddenly bogged down to an idle. Idles but will not power up and shuts off or runs rough. We have done following:

1 - compression checks 130 lbs+ each cyl. (Cold)
2 - replaced fuel lines and primer bulb
3 - replaced fuel with fresh NON ethanol fuel (e10 has been used in past where unavoidable)
4 - carbs removed and cleaned (they looked fine to me)
5 - fuel pump rebuilt (again-old parts looked fine)
6 - inline fuel filter replaced

Our motor problem appears to be fuel starvation but none of above has fixed the trouble or even made it better.
So, what else is there to check in the fuel system?

Help requested. Where and what should I look at next?

Thanks in advance.

 

[1nebel0]

Re: Mercury 90hp 2 stroke has me at ropes end!

Do you have spark on all three cylinders? From that point you can then say it's a fuel problem....I bet you lost spark...let us know.....

 

[ddwyer]

Re: Mercury 90hp 2 stroke has me at ropes end!

I would check all three coil packs as well....

 

[ddwyer]

Re: Mercury 90hp 2 stroke has me at ropes end!

Oh yeah. Run a can of Seafoam through the fuel system. You may have some water or condensation in the tank which can cause a "dead spot" while you're underway, and in turn, bogging the engine down.

 

[lt4247]

Re: Mercury 90hp 2 stroke has me at ropes end!

Oh yeah. Run a can of Seafoam through the fuel system. You may have some water or condensation in the tank which can cause a "dead spot" while you're underway, and in turn, bogging the engine down.

Thanks for the response. I have been all through the fuel system and also ran boat on the water with remote tank with new non ethanol fuel = no help. Have appointment with mechanic to find and fix the problem on 5/20. I will post in detail what we find.

 

[Texasmark]

Re: Mercury 90hp 2 stroke has me at ropes end!

I have that engine year and size. Iterating what you said, you were humming along for a minute and suddenly it bogged down and would only idle or die. Did you check the primer bulb and did squeezing it help any? Was it semi firm when the engine was running?

If yes to the above then lets move on.

Do you have a timing light? If not, borrow one or spend the money you would have spent at the repair shop on May 20 and get one. Autozone has a battery operated one with part # CP7527 for $39. If that's out of the question then there are other ways to check spark, but this is the easiest and by moving the sensor toward and away from the sp wire, you get an idea of intensity of spark and can easily compare cylinders. If you want to talk about other ways to do it we can do that but I have one and do it and it's quick and painless and prefer it.

Hook it up to it's power source as directed. Start the engine and let it idle; muffs fine. Move the sensor for the timing light adjacent to each plug wire. You don't need to touch the wire just get close. If all CDI's are putting out high voltage, the light will flash as you approach each spark plug wire. If one doesn't respond you have your smoking gun.

Assuming they all work, then you are in fact chasing fuel.

When you removed the carbs did you notice the brass plug in the bottom of the bowl? Did you blow compressed air through it in both directions? That is your high speed jet. If plugged it will shut down that cylinder. As on mine you may not see the foreign object with just your eye. On mine they looked good as did the carb bowls, pristeen clean.

However when I hit #3 carb bowl with compressed air in both directions focusing on the high speed jet, lo and behold a pice of crud popped out into view. That was my smoking gun. Clearing that out solved my peculiar operational problem at high speeds.

Even though you may have one carb contaminated, if that's the problem, depending on the load on the engine.....boat size, load in the boat, loosing that one cylinder (lost 1/3 your HP) could load up the other two trying to run and bog them down as you mentioned. 2 strokes do not like to be bogged down and they just give up.

Take a look and come back.
Mark

 

[lt4247]

Re: Mercury 90hp 2 stroke has me at ropes end!

WE FOUND THE PROBLEM!
And I kind of feel like a dunce. The symptoms all pointed to fuel starvation but as noted in my first post, I went through the fuel system with no improvement. I met with the mechanic at the river and described all I had done to date and that i believed we had an ignition problem of some sort. He started the motor and idled it. OK..... He then asked:"you test the plugs"? "Uh, no they looked fine to me". It is a 2002 model with no more 100 hours(!?). (Note: starting to feel a little inferior and sick at this point!)

He tested the plugs at idle and 2 were dead! DANG! How could i have over looked this? He screwed in three new plugs and it idle just fine and took off full throttle like a raped ape! He explained plugs go bad over time especially with our crap fuels. He checked timing, etc just to make sure and all was now OK. Sensing my feelings of stupidity, he charged me a minimal service charge. As I walked away he said: "remember, plugs first on outboards".
Lesson learned and not soon forgotten. Now back to fishin!
Thank you all for helping out.