2002 75HP 3 cyl Mercury Outboard bogs down at full throttle

Nicculus

Cadet
Joined
Aug 27, 2020
Messages
6
Hello all! New to this forum and just bought a used McKee Craft bowrider. My issue, to start, was the boat only went trolling speed when full throttle. Found there was an issue with the fuel line leaking at the coupler that couples the fuel line from the gas hand pump to the short fuel line going into engine. I fixed that. I noticed the air/fuel screws on carburetor (this has a carb tree. 3 stacked) were possibly out of whack. One screw was 1 1/2 turns from seating, one was 14 turns from seating and the other was like 5 turns from seating. I got those in sync while using muffs at home. I was ready to put it in the water to adjusted them with a load on the prop but before I left, I fired the engine up on the muffs. I noticed gas slowly leaking out the open hole on the carb, just to the left of the air/fuel screw (see attached pic). Just to test, I turned all air/fuel screws on the carb clockwise and lightly seated them. I thought the engine would choke out but it didn't?!? It may have been running higher RPMs when all 3 were closed. So, why didn't the engine choke out with all 3 air/fuel screws closed? Also, why is gas trickling out of the open hole next to the air/fuel screw? Thank you for helping
 

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Nicculus

Cadet
Joined
Aug 27, 2020
Messages
6
This morning, I dropped a second can of seafoam in the gas tank and hit the air intake on all 3 carbs with a full can of carb cleaner, while bumping the RPMs up a smidge from idle (on land with muffs). I didn't see gas leak out of that hole today. The engine sounded great today. Got it in the water. It ran a tiny bit better. I was also tuning the air/fuel screws while out on water but still bogs down at full throttle. I was also able to hook up my buddy's gas can to it and it ran the same, bogged at full throttle. So, I know it isn't the fuel, lines, or bulb. I am getting 3 new spark plugs tomorrow. Other than that, I am not sure what to do short of pulling the 3 carbs off. I was hoping to exhaust all avenues before I take that on.
 

appleo

Petty Officer 1st Class
Joined
Jul 19, 2012
Messages
388
Curious. was it the bottom carb leaking out the tiny hole?

Mine. was. bottom carb was full of gunk top carbs were not .
 

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Nicculus

Cadet
Joined
Aug 27, 2020
Messages
6
appleo,
It was the top carb leaking out the air vent next to the idle fuel/air screw. It hasn't done it since, though. I don't know what changed because I still have the same issue of bogging down full throttle. I ordered 3 gasket kits and will be taking the carb tree off to clean them. I tried everything else.
 

Nicculus

Cadet
Joined
Aug 27, 2020
Messages
6
I ended up taking the carbs off and cleaning them. There was some gunk and trash in them but not crazy. The old gaskets looked rough and that might have been the issue. Swapped all gaskets. The carbs are brand new again. About to take it for a water test next chance I get. I am hoping this resolved the issue of bogging down when full throttle and ends up at a trolling speed.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,896
Waiting on your fuel filter contents report. If the crud in your carbs included black bits, you might as well get new fuel lines in the engine as that is what the black specks are.
 

Nicculus

Cadet
Joined
Aug 27, 2020
Messages
6
I am happy to report the boat went full speed with fully throttled!!!!! It was the carbs. Most likely, the gaskets were dilapidated and allowing air in. The old fuel filter only had 1 black spec in it. The previous owner may have swapped it before I bought it, though. Felt good to be going full speed! This is my first boat and I have never messed with carbs on anything so I am ecstatic. This motor runs like new again and I got a hell of a deal on it. Thank you to everyone, especially Texas
 
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