Mystery of the disappearing O-ring


I am missing the o-ring that goes on the end of the carb side drain screw on my 2000 wr400. Conveniently, the screw and o-ring are conspicuously absent from the parts diagram. See red circle in pic above. That's where the screw with attatched o-ring are supposed to go. I have been to the local bike shop three times now.

I need this o-ring!!!

No oring used. The screw has a slightly conal tip that closes off the passage way from the bowl to the drain line. I have only seen the screw come with the bowl, though some carb parts places may carry them. It is not considered a normal service item.

I concur with William. There's no o-ring for that screw. The copper tip should seal and prevent gas leaks. If you are leaking gas it could be your float valve. I took my wr400 carb apart and had the same concern but after many hours of inspecting the carb bowl I realized there's no o-ring seal. My carb was leaking and the float vavle was the culprit.

Despite making a fool of myself in my assumption, your replies have helped me realize that must be the problem. Some other o-ring in my recent memory must have got me off track. I will be ordering the needle set asap.

The diagram sure doesn't have the screw in it, so that kind of threw me through a loop as well.

I appreciate your help and hopefully soon I will be tearing it up on my favorite blue machine once again.


Try Sudco for the carb parts. Yamaha wants to sell the whole needle/seat assembly. Sudco will sell just the needle. With the rubber tip on the needle, the seat almost never goes bad. Make sure you order the O-Ring that goes around the needle seat as soon as you take the seat out of the carb, that O-Ring will start to leak, and then even if your float is set right and the needle is good, you will still leak past the O-Ring and overflow the float bowl.

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