Old Mercury Outboard Question

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JohnnyD

Senior Member
I’m shamed to admit I know the bare minimum when it comes to outboards, especially older ones, so I’m just going to toss this out there for my own curiosity. I’ve been running my grandfather’s old 1993 50 HP 2 stroke Mercury and boat since he left it to me over a decade ago. Works fine, runs great. I have, however, noticed that I get some gas leaking under the cowl of the motor when I trim the motor up. We’ve just recently had work done on it (Carb job, new fuel pump, lines). We’ve had it re-checked since then since I was a little concerned about that, but was told by a few sources that sometimes those old motors drip a little fuel because the float in the carb just can’t stop it all when the motor is trimmed up. Thoughts? All lines and connectors check out. No problems priming the bulb. Boat starts and runs fine. I’ve basically had the fuel system checked twice and it all seems fine.

Now, it is not a large amount of fuel. Just enough for me to see a little slick when I take the cowl off the top of the motor. And it’s always when I return home after having the motor trimmed up for the drive back so I’m assuming that’s when it’s happening. Probably on the trip to the lake as well.

I’ve got a little perfectionist streak in me so I just wanted to see if this seems normal or if I should look closer at a potential issue.
 

WayneB

Senior Member
totally normal.
If it bugs you, or you want to avoid having a slick around the boat when you launch, disconnect the line from the engine at idle and let run a couple minutes to lower fuel in bowls.
I would avoid running till it quits, just to ensure you keep the cylinders lubed.
In this case, your sources are correct. ;)
 
totally normal.
If it bugs you, or you want to avoid having a slick around the boat when you launch, disconnect the line from the engine at idle and let run a couple minutes to lower fuel in bowls.
I would avoid running till it quits, just to ensure you keep the cylinders lubed.
In this case, your sources are correct. ;)
How long can the motor stay running if there is zero fuel mix in the cylinder? Not long. You can run it out of gas completely without harming your cylinder and it won’t start till fuel is in the cylinder again.
The lack of oil and running is where the problem would occur not lack of gas.

As for the Op his gas is probably leaking out the vent when tipped up.
Not “normal to leak gas” on any motor.
 

WayneB

Senior Member
How long can the motor stay running if there is zero fuel mix in the cylinder? Not long. You can run it out of gas completely without harming your cylinder and it won’t start till fuel is in the cylinder again.
The lack of oil and running is where the problem would occur not lack of gas.

As for the Op his gas is probably leaking out the vent when tipped up.
Not “normal to leak gas” on any motor.
at a 50:1 ratio; oil is little more than a trace in the fuel as is. Shutting off before it starves out will leave a little oil film on cylinders which is significantly better than no film.
Overflow from the vent is the likely culprit, if it has a carburetor and you tilt beyond the normal 'in use' limits of the design, it will drain off.
 

rayjay

Senior Member
When idling around you end up with a good bit of oil and gas in the crankcase as there is just not enough pumping action going on. If the op disconnects the fuel line and runs [ at idle ] the float bowls mostly dry there will be no bad side effects. On the other hand, running the tank / float bowls dry at high rpm is to be avoided although the effects on a cool running boat motor would be less than an air cooled motor like a chainsaw.
 
You might want to have your Reeds checked. My 97 did this and I opened it up and found a few pieces missing. Lucky they were to small to cause any damage. Replaced the Reeds and no more leak.
 
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