Fuel leak in cowling on '89 Mariner 75

[flyboyo2]

Hello all,

Christmas break is over so back to the boat.  It's getting a little chilly here in PC so I just backed my boat into the garage from the carport.  I'm sure glad nobody was around to witness that goat rope. It was the first time I backed a boat trailer since 1974.
The problem  now is when I tilted the engine full up to move the boat there obviously was a fuel leak because when lowering the engine a considerable amount of oil mixed fuel leaked from the front of the cowl.  No leakage when the motor is verticle. Assuming that the culprit is a carburetor and since I don't speak carburetor what is the most likely problem or what else would cause the leak?

Your Obedient Servant

[RickK]

Congrats on breaking up the ring rust on backing a trailer - kinda like riding a bike
I think that the "fuel leak" is somewhat normal with carb'd outboards.  It happens on mine quite often when I tilt it forward.

[flyboyo2]

Thanks RikK, I bow to your superior knowledge.

[RickK]

I'm sure that someone can add some more sound advice to my reply, like why it does this 

[fitz73222]

Flyboy,
Remove the cowling, remove the 6 attenuator box screws to expose the carburetor throats. Squeeze the primer bulb with the fuel line connected to the engine and see if gas comes out of the carbs. Next, tilt the engine and observe if they leak excessively; continue looking at all the connecting fuel hoses and tubing mainly on the port side of the engine and look for leaks. If you have been using ethanol based fuel, all of your fuel lines and fittings maybe suspect.

[flyboyo2]

Fitz, thanks for the tip, I will do this at my first opportunity.

[dburr]

Fly I have/ had the same issue with an 89 Merc 70 on a Sport15 Whaler which I beleave is the same carb set up, if so, the problem you have is with the bowl vents. For what ever reason they were drilled in the card throat and have a very small bronze tube that is angled towards the front of the carb. At full tilt they will leak, and that is that.

The way I keep fuel from running into the boat is with a small piece of IV tubing shoved over each of the vents and then led up to the top of the air box and then out through one of the air inlet holes. It took a while to figure out the best lead to keep gas from leaking..

 I used to have them run out the bottom of the cowling but anytime the engine was tilted full up there was a nice anti mosquito sheen behind the boat and the Coasties don't like that.  Another problem was when I opened the cowling and was not careful how it was closed, the tubes got pinched and then she ran terribly..

[flyboyo2]

dburr,
Thanks for the tip.  I did the check suggested by Farley and with the engine vertical there was no leakage.  As with you my Mariner 75 only appears to leak when tilted full up.  Do you happen to have the specs on the tubing that you use?

Thanks for the info.

[fitz73222]

These engines typically do not leak when tilted up. The same carbs are used on 75,90,100,115, and 125 models. The main problem you have is leaking needle and seats in one or all three of your carbs. That said, all engines will have a small amount of residual fuel but it should never be leaking into the boat as you describe.

[flyboyo2]

Farley,

I just did the squeeze the bulb routine again and there is, in fact, a very small amount of residual fuel in the middle carb. The fuel amounts to a  slight amount at the very bottom of the butterfly.  The other two carbs are clean. I could find no leakage in the fuel pump area.  I estimate the leak to be a couple of ounces at the most, enough to make an oily mess. I assume this means a carb rebuild.