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Author Topic:   1978 Mercury Outboard Leaking Fuel

msarafin posted 12-05-2005 03:53 PM ET (US)
I have a 1978 Mercury 80-HP outboard that is leaking fuel from the jet in the lower of the two carburetors. [How can this problem be solved?]
Binkie posted 12-05-2005 04:21 PM ET (US)
If you go to John`s Old Mercury Website,
http://www.pfs-ware.com/kwast/ They will help you. They`re a nice bunch and many are professional Mercury mechanics. If you own and old Mer. its a good place to hang out.
outragesteve posted 12-05-2005 07:24 PM ET (US)
Possible stuck/bad float.
sosmerc posted 12-05-2005 08:26 PM ET (US)
Have you removed the jet? (the actual jet is inside the jet holder...which is the brass piece with a 1/2 inch hex that you can see at the bottom/front of the float bowl. There is a thin gasket between this holder and the float bowl. Replace the gasket and see if it still leaks. What may look like a leak from that area is actually fuel spilling out the front of the carb and running down into that area. (this could be from debris getting into the carb needle/seat, or as said before, a stuck float...or a sinking float.
Try this...remove the bottom jet holder. Then pump clean fuel through the carb with the primer bulb...just let the fuel pour out through the hole in the bowl. If you get lucky, you may flush out debris that was causing the problem. Re-install the jet holder with its gasket. Then reprime the carb gently and see if it still leaks.
BEFORE TRYING TO START THE ENGINE, CAREFULLY CLEAN UP ALL THE SPLILLED FUEL THAT HAS COLLECTED IN YOUR BELLYPAN...USE WATER TO FLUSH THIS OUT CAREFULLY...WITHOUT GETTING ANY WATER INTO THE CARBS OR ON THE IGNITION PARTS.
THE SLIGHTEST SPARK CAN IGNITE FUEL VAPOR...SO PLEASE BE CAREFUL.
An engine of this age may have fuel leaks around any of a number of hose fittings....and if the engine hasn't been serviced for years it's probably time for new inlet needle and seats, and new floats and carb gaskets.
It's not a terribly difficult job...maybe 3 hours from start to finish including testing and adjusting.
msarafin posted 12-08-2005 11:28 AM ET (US)
Thanks to all for the good info...

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Author	Topic: 1978 Mercury Outboard Leaking Fuel
msarafin	posted 12-05-2005 03:53 PM ET (US) I have a 1978 Mercury 80-HP outboard that is leaking fuel from the jet in the lower of the two carburetors. [How can this problem be solved?]
Binkie	posted 12-05-2005 04:21 PM ET (US) If you go to John`s Old Mercury Website, http://www.pfs-ware.com/kwast/ They will help you. They`re a nice bunch and many are professional Mercury mechanics. If you own and old Mer. its a good place to hang out.
outragesteve	posted 12-05-2005 07:24 PM ET (US) Possible stuck/bad float.
sosmerc	posted 12-05-2005 08:26 PM ET (US) Have you removed the jet? (the actual jet is inside the jet holder...which is the brass piece with a 1/2 inch hex that you can see at the bottom/front of the float bowl. There is a thin gasket between this holder and the float bowl. Replace the gasket and see if it still leaks. What may look like a leak from that area is actually fuel spilling out the front of the carb and running down into that area. (this could be from debris getting into the carb needle/seat, or as said before, a stuck float...or a sinking float. Try this...remove the bottom jet holder. Then pump clean fuel through the carb with the primer bulb...just let the fuel pour out through the hole in the bowl. If you get lucky, you may flush out debris that was causing the problem. Re-install the jet holder with its gasket. Then reprime the carb gently and see if it still leaks. BEFORE TRYING TO START THE ENGINE, CAREFULLY CLEAN UP ALL THE SPLILLED FUEL THAT HAS COLLECTED IN YOUR BELLYPAN...USE WATER TO FLUSH THIS OUT CAREFULLY...WITHOUT GETTING ANY WATER INTO THE CARBS OR ON THE IGNITION PARTS. THE SLIGHTEST SPARK CAN IGNITE FUEL VAPOR...SO PLEASE BE CAREFUL. An engine of this age may have fuel leaks around any of a number of hose fittings....and if the engine hasn't been serviced for years it's probably time for new inlet needle and seats, and new floats and carb gaskets. It's not a terribly difficult job...maybe 3 hours from start to finish including testing and adjusting.
msarafin	posted 12-08-2005 11:28 AM ET (US) Thanks to all for the good info...