2004 Mercury 115 ELPTO surging

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aidanmurphy

Petty Officer 2nd Class
Joined
Apr 2, 2022
Messages
107
Hey everyone, picked up a new to me 2003 Key Largo 180cc. Super clean boat and came with the 115 2 stroke Mercury.

The motor idles perfectly and has great holeshot and does not bog down at all.

However, upon pushing at higher RPM, the boat feels like it is surging or will not hold high RPM. It will cruise well, but there is still the occasional surge that is almost imperceivable. However when pushing for the last 1/4th of throttle the boat just falls back down.

Previous owner said he cleaned the carbs, replaced the fuel pump. I checked the fuel pickup and the fuel filter and both are clean. I stuck a scope in the pickup into the tank and it doesn't look spotless but it doesn't look terrible either. Anywhere I should be looking in particular?

The tachometer also does not work.
 
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Mc Tool

Petty Officer 2nd Class
Joined
Aug 7, 2024
Messages
195
Sure does sound like a fuel flow issue .
Get the carbs primed up and remove fuel feed hose from carbs and direct at a suitable container , start engine and confirm that fuel is being delivered at a reasonable pressure ( put finger over end of hose and try and make it spray a bit ). The longer you can continue this test the better as the fuel may flow well initially and them taper off . .
If someone has had the carbs apart ( like the PO ) you pretty much gotta make sure he hasnt cocked it up , like float levels
When you say "falls back down " do you mean all cylinders start failing , or does it start loosing only a couple of cylinders ?
The fact that its ok at 3/4 throttle but not full *** does sound like feul BUT dont get tunnel vision .
If you have another fuel hose , from tank to motor, try that .
 
A

aidanmurphy

Petty Officer 2nd Class
Joined
Apr 2, 2022
Messages
107
Thanks for the response. I was thinking the same thing.. If PO says he went through the carbs I better make sure it was done correctly.

When I mean "falling off" I mean the boat will get to say 4500RPM and then drop back down to 4000RPM, even if you keep adding throttle. I agree it does sound fuel related, but I have new spark plugs and wires coming just to cross off some intermittent spark issues. The boat idles great, will never shut off and has what feels like full power coming out of the hole. It is just the top end band mainly that it can't reach.

I will plan to do that carb trick and maybe take them off to check the work that was done.
 
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racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,243
Correct.-----The bulb is a simple manual pump.-----It can be a useful trouble shooting tool.-----The fuel pump on the motor is also easy to inspect / install a repair kit.-----Oil injection has been tested ?----You have installed a new water pump impeller when you got the boat ?
 
A

aidanmurphy

Petty Officer 2nd Class
Joined
Apr 2, 2022
Messages
107
racerone said:
Correct.-----The bulb is a simple manual pump.-----It can be a useful trouble shooting tool.-----The fuel pump on the motor is also easy to inspect / install a repair kit.-----Oil injection has been tested ?----You have installed a new water pump impeller when you got the boat ?
Click to expand...
PO installed new impeller, it pisses strong. PO also said he installed a new fuel pump. Visually it looks new, I can pull it apart if moving to a new aux fuel tank + new plugs and wires doesn't help anything. That is going to be my next step.

I have not directly tested oil injection but when I looked at the plugs they were a tad oily and didn't look leaned out.

What is the best way to directly test the oil injection?
 
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