Off topic - 1975 Yamaha TY80 carb issue

[GIJoeBob]

I have a 1975 TY80 (two stroke trials bike) my 8 year old rides. It started having issues (not getting fuel) so I rebuilt the carb.

After putting it back on it starts up great but immediately revs to a very high rpm like the throttle is being held wide open.

As far as I can tell the carb slide and cable are operating properly and the engine is reving while the carb slide is seated all the way in the carb.

The idle adjustment screw is just barely screwed into the carb and is not touching the slide.

Any ideas on what could be going on here?

Thanks.

[mookie]

air leak elsewhere.
are you certain that the slide is in correctly?
can you see it moving up/down from the back of the carb?

intake manifold cracked?
squirt with WD /brake cleaner while running and see if it changes revs.

weather strip cement will seal it from the outside.
allow to dry...

leaking crank seals?-not likely if it starts o.k.
i too have a TY80!!

rotsa ruk

[GIJoeBob]

air leak elsewhere.
are you certain that the slide is in correctly?
can you see it moving up/down from the back of the carb?

intake manifold cracked?
squirt with WD /brake cleaner while running and see if it changes revs.

weather strip cement will seal it from the outside.
allow to dry...

leaking crank seals?-not likely if it starts o.k.
i too have a TY80!!

rotsa ruk

The slide is in and operating correctly. I will check for air leaks but I don't think any of the seals are suspect.

[mookie]

start it and squirt something onto the intake and see what happens.
will it run with the bellmouth covered?

[GIJoeBob]

I revisted the bike this weekend and figured it out. There is a plastic bushing that fits between the intake tube and the throat of the carb that was not seated all the way that was making the bike run lean.

I fixed that and ran the bike around the yard and churned up dirt and grass much to the delight of my children.

Thanks for the help everyone.