Fuel tap leak

Started by legacybrg, March 05, 2020, 06:42:18 AM

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Hi all, very frustrating time with a persistent leak. Fuel is dripping from the locating screws, not from the tap mechanism. Both screws appear original and have two washers, one flat one split. The parts diagram shows just one flat washer so I've ordered new Yamaha screws and washers. Any ideas why this is happening and will replacing the fixings cure the leak?


Replacing the screws and washers probably won't fix it. If the petcock itself isn't leaking, there is a neoprene 'O' type gasket between the tank and the petcock that probably needs to be replaced. Does the petcock look original?
Whale oil beef hooked!

kevin g

Aren't the screws supposed to have a fiber washer between the screw and tank?  I think a flat and lock washer have no chance of sealing.  The screw holes in my '83 go clear through into the tank and no screw can seal without a fiber washer.


You are correct. There are 2 washers and 2 fibre washers that actually do the sealing. Without the fibre washers fuel will leak and I would think pretty bad.

The Prophet of Doom

Watch out for rust under the ring gasket - that's a recipe for leaking.  If you need to, some rust converter, block sand it till it's flat, then a nice new layer of epoxy paint.
You can replace fibre washers with square cut viton if you haven't saved them. I always use blue loctite on the screw threads as well.


Many thanks for the replies and advice. I replaced the screws and washers with genuine Yam parts and that seems to have done the trick. The washers are a soft gasket type. Why metal washers were fitted and why they have only just started leaking I have no idea. Anyway, on with the rebuild - the carbs are due back soon having been given a complete strip down, clean and overhaul, a job beyond my knowledge and resources I'm afraid. I will be fitting an inline fuel filter - any recommendations?