Trouble with 06 Mercury 3.5hp

[Bstnsportsfan]

I saw my 18 year old nephew this morning and he has a little Jon boat with this 3.5hp motor that is giving him some trouble. He’s trying to avoid spending $$$ as he only paid $200 for a motor.

It starts fine and runs in idle but upon giving it gas it stalls. A second issue is oil leaking from the lower unit. Looks like where two plastic pieces come together (see pics).

Any idea what would cause the motor to stall upon power being applied?

Thank you!!

[massbay]

That's my old boatyard on liberty st. I sold it to those guys in 2001.
that motor is 1400 mi from home.

[blaster]

As far as the stalling goes it sounds like the carburetor needs to be rebuilt. The gear lube leak is the bigger problem. It could be as simple as a bad or loose seal. Hopefully the seal surface is not damaged causing the leak. Unfortunately you have to go through it with some mechanical work. No magic fix.

when you open the drain plug for the lower unit is there any water?

[LFBB]

Yup, first thing is check the carb.

I'm hoping a gasket for the lower unit, that is better then a crack. Was it leaking when he bought it?

[Bstnsportsfan]

I’ll have to check with him but I don’t believe it was leaking. He used it a few times and he crapped out the most recent time. I think he should have a mechanic take a look but he’s trying to save a buck which I can’t blame him.

[LFBB]

If he's mechanically inclined have him watch a few youtube videos and take a shot at it. If he's not, might want to let a pro do it and save in the long run.

[Sans Peur]

I couldn't really tell from the picture but, are you sure that is gear lube? It could be a secondary issue from the carb. If he is having carb problems that could be 2 stroke oil running down from the engine. Is it really wet and oily up under the engine?

[Bstnsportsfan]

I just looked at it briefly it is a bit oily around the engine. I believe the motor is a 4 stroke but I could be wrong. The oil appears to be leaking from a “joint” in the lower unit but not sure if it’s coming down from the top and that just were it’s showing. Or if that is the source of the leak.

[DaleH]

MODEL - With that 2-piece cowling, I'd bet $$ that is the newer 4-stroke model. But have him confirm the serial number (s/n) and if is 0R131842 or above ... then it indeed is a 4-stroke model. Then go here for detailed schematics: https://www.marineengine.com/parts/m...5-4stroke-carb

That site will link you to other Merc model by year, from here ... just in case she's not a 4-stroke: https://www.marineengine.com/parts/mercury-outboard/index.php


CARB - Good idea to clean it ... but from smallest orifices to largest, never clean it the wrong way or you can create further blockages. My 1st option is to drain the carb and fuel tank and fill the carb with a small amount of Seafoam, but remove the kill lanyard or plug so she can't start and pull it through to ensure you fill the carb with treated fuel. If it has a drain plug, check it and make sure you filled the bowl. Let soak for a day or two. Then drain that stuff all out and try again with new fuel. It isn't a magic elixir curing all ailments and/or Covid, LOL, but it has worked for me before.

These can be finicky OBs if someone previously FUTZED with it and played with the adjustment linkages or the idle mixture instead of the idle speed screw. The idle RPM or speed screw typically has a spring on it and operates more as an 'throttle stop', in that it sets where the throttle can be set. It does not play with the mixture. I've seen these smaller HP 'carb'd' 4-strokes (not EFIs) from Merc, Honda, Yamaha and Tohatsu all have issues when opening up the throttle, but the butterfly isn't opening to correspond, as someone had played with the adjustments; Yummies being the worst in linkage and/or adjustment design. But 1st things 1st ... try a good carb cleaning, by injected solution then possibly a bench cleaning. We had one Yumster at our boat club where the only solution was a new carb ... and presto, she now runs again! And yet that one uses a remote tank fed by a micron-rated fuel filter - go figure.


OIL - The lower unit for gearcase oil is sealed BELOW that joint. Where this appears to be a 4-stroke, it could be crankcase oil dripping down the inside of the power leg?


NOTE - These 4-strokes are VERY PARTICULAR for how they are stored! For example, on old 2-strokes, we could remove them and lie them on their back. Not so with 4-strokes! In fact, they should only be stored either in the (1) vertical position as if in use, or (2) on their side, but he needs to check for WHICH SIDE should be up! If he stored it wrong, the motor could have spilt oil out unintentionally and now it is running down inside the lower leg and exhaust column.

Uhhhh, has he checked the oil level at all?

Best I can do via cyber-space ....