Hi, my lads TXT 50 sometimes, has a bit of a sh*t fit and the revs either stick rather than drop off when the throttle is released - or sometimes even increse to the point where the bike's screaming (this usually happens after my lad falls off and the bike's on its side).

Any ideas what could be causing this, and what a suitable fix would be?

Cheers - Boner.

water in the carb, a weak spring, throttle body maybe has some grit in? just my thoughts!!

You might try looking at the sparkplug if it's lean look to the base gasket or carb manifold for leaks. I had a KTM 540 with this problem and it was the base gasket.

Air leak? My Beta did this once - would rev right up in neutral with the throttle shut, and thats what it turned out to be.

check the obvious things first, kink in the throttle cable, smooth operation of the throttle, grit between the throttle tube and the handlebar, etc.

With the engine idlng, spray some contact cleaner around the intake manifold... if the revs pick up you have a leak and that can cause your problem.

Not likely but still possible is a lot of wear on the carburetor slide / bore allowing the slide to 'vibrate' and hang up coming down, especially if the return spring is a little weak. I had this happen on an old Bultaco Sherpa T years ago and it took me a long time to figure out what was going.

Also make certain that the fuel petcock / fuel filter is clean, allowing the correct amount of fuel supply to the engine. I had a TM-400 Suzuki once that I MADE SURE I never ran out of gas on, (again) as just before it quit running the bloody thing would lean out and the revs would head for the moon, with me trying to hang on until it ran completely out and would quit. Changed into my brown underwear more than once on that bike before we parted company.

Great - thanks guys, I'll take a look at those bits.

Wouldn't be suprised if it was water in the carb.

My boy gets a bit over-keen with the old hosepipe!

Cheers - Boner.