XS400 New Member
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My 1977 xs400 needs throttle shaft seals to be replaced. Does that mean it needs a full carb rebuild?
The previous owner said he "rebuilt the carb not too long ago." I'm guessing he either overlooked throttle shaft seals or used bad ones.
What do y'all think?
I see them in the service manual, would imagine that they would be trash after carb spray hit them.
they were trash before carb spray hit them haha.
but i see now how that could have exacerbated the problem.
anyway, should I do a full rebuild or not?
Have there been any other issues?
I'd give them a good cleaning since you'll have them apart anyways.
Unless there's obvious wear you probably don't need to replace much else.
Gaskets are cheap so that might be worthwhile.
You'll probably make a mess of the screws holding the butterfly plates (the screw threads get pinched in the factory to keep them from coming out) so it might be a good idea to have replacements ready.
Be careful with the plates too. Replacements are almost nonexistent.

The butterfly shaft seals can still be bought from Yamaha dealers. There are aftermarket replacements but some are known to be inferior.
I did find a source for the screws and viton butterfly shaft seals that seem like good quality. Haven't put many miles on them yet.
There are some past threads with most of the part numbers.