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Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I have a 2001 90 hp mercury 2 stroke. Low hour, fresh water

Customer Question

John, I have a 2001 90 hp mercury 2 stroke.
Low hour, fresh water engine.
While running boat one day I started losing power and had to push throttle wide open to maintain 4000 rpms and keep boat on plane. Engine never quit, idled fine and started fine.
This was intermittent to start as it didn't happen again until a couple of runs later now it will not go over 4200 with just myself in boat. Before this happened it would turn 5500 with no problem.
I cannot get up on plane now if boat is loaded. I put a smaller diameter wheel on, 17 vs a 19 and it will let me get up on plane with a load in boat but will still not turn over 4500 rpms.
Stator ?
Submitted: 1 year ago.
Category: Boat
Expert:  Charles replied 1 year ago.

Hello, my name is***** will assist you today.

Would you please post the serial number of the engine?

Have you done any troubleshooting already?

You will need a good quality multimeter to test the ignition system, do you have one?

Customer: replied 1 year ago.
2002 90 ELPTO
I do not have a multi meter
Expert:  Charles replied 1 year ago.

Got it thank you.

There are still several items that can be checked without a meter. Are you ready to begin?

Customer: replied 1 year ago.
Expert:  Charles replied 1 year ago.

Alright, the first item to check is the fuel. Make sure that you do not have any water in it.

Then remove all 3 plugs and look at the tips, are they all the same color?

Have a helper crank the engine over, while you have the plugs inserted into the plug boots and make sure that all 3 cylinders have spark. You will need to do 2 at once. 1 and either 2 or 3, 2 and 1, then 3 and 1. The grounding system on the electronics is rather unique on this engine.

Let me know what you see.

Customer: replied 1 year ago.
Should have told you first , sorry, all plugs, wires and coils have been checked by a mechanic and problem still purists
Expert:  Charles replied 1 year ago.

Did he also do compression? If so, do you know the numbers?

Expert:  Charles replied 1 year ago.

What plugs are in the motor now?

Was the mechanic a marine tech, or an auto tech?

Customer: replied 1 year ago.
130 all 3 cylinders
Fuel is fine, non ethanol premium with an additive
Expert:  Charles replied 1 year ago.

Has your engine been sitting some time unused?

Does the alarm system still function?

Customer: replied 1 year ago.
NGK BUZHW-2 brand newIt sat for about a year, I started using it in October. Had to replace fuel pump diaphragm but nothing else .
Alarms work, yes.
It starts and idles fine, just no top end power.
I did notice the tach fluctuating on several different occasions when this first started.
The mechanics is a certified mercury tech
Expert:  Charles replied 1 year ago.

Got it.

When the issue happens, has the engine been running for a bit?

Do you need to use a battery charger when you return at the end of the day?

Customer: replied 1 year ago.
When it first happened it had warmed up and I took off, got on plane with no issue like I always had and about 5 minutes in running at 4000 Rpm the power started to fall off. I pushed it wide open and it stayed on 0lane but only turned 4000. Never cut off when I stopped, idled fine and restarted fine.
It happened a couple of times and now it stays there 4500 wide open. It would not get on plane with the boat loaded and struggled with just me until I went to a 17 prop.
It was never an issue before I lost the upper rpms. Always got on plane and would turn 5500 with a 19 prop loaded or not.
Expert:  Charles replied 1 year ago.


When you turn the key on, you do hear the alarm test beep?

Customer: replied 1 year ago.
No, I hear nothing.
I do not need a battery charger. It is charging fine.
Expert:  Charles replied 1 year ago.

Ok, lets trick the alarm into going off..

Locate the tan/blue wire in the engine harness. With the key on, engine off, unplug the connector coming from the head sensor. Ground out the harness end of the connector to a good clean engine bolt. You should hear a solid tone alarm.

Customer: replied 1 year ago.
got an alarm
Expert:  Charles replied 1 year ago.


Can you remove all three plugs and look at the tips of them? Or send me a pic of them?

Customer: replied 1 year ago.
Mechanic replaced plugs and tried new coils to see if it made a difference and it did not.
He said it might be possible the stator is not producing enough spark on the high side to give it the higher rpms, high side bad and low side still good.
Customer: replied 1 year ago.
Left one is top cylinder
Expert:  Charles replied 1 year ago.

Thanks, ***** ***** is not firing/burning correctly. Number two is barely doing so and number 1 is fine.

When at idle, does the motor leave a sheen in he water?

Customer: replied 1 year ago.
No, it does not
Expert:  Charles replied 1 year ago.

Do you have access to a water hose and a set of flushers so that you can run the engine?

Customer: replied 1 year ago.
Hooked up and ready to run
Customer: replied 1 year ago.
Hello, Charles ?
Expert:  Charles replied 1 year ago.

Sorry, had to step out for a bit. I am back online now.

Start the engine and just let it idle. Remove one plug boot and note the RPM change on the engine. Then replace that wire and do #2 and 3. The drop should be the same for all 3.

Please let me know how this goes.

Customer: replied 1 year ago.
Charles, it's dark outside now so I'm done.
Your last response to me was at 3 12, over 2 hours ago. You kind of left me hanging.What you are asking has been done already and it made no difference
As I stated earlier, it starts fine, it idles fine, it just does not tach up past 4500
Expert:  Charles replied 1 year ago.

Ok, what color i the fuel line to the engine? If it is gray, what color is any writing on it?

Customer: replied 1 year ago.
All new fuel line
Racor water seperator
Expert:  Charles replied 1 year ago.

Have the carbs been cleaned as well?

Customer: replied 1 year ago.
it is not fuel related in my opinion because it runs smooth and does not miss a bit.
Again, can the stator cause this ?
Expert:  Charles replied 1 year ago.

It could be, you will need a good digital multimeter to test it

Customer: replied 1 year ago.
There is nothing visually leaking from the stator, how to I go about testing it with a meter ?
Expert:  Charles replied 1 year ago.

You would need to disconnect it and test between the green and the white leads for both resistance and voltage when cranking.