Hi just wondering if anyone can help I have a beta 125 2004 trials I went out today and revs stuck on full and I pulled kill switch no joy still didn’t cut out so had to put ht cap off checked carb and throttle in fine not stuck not nicks in cable slider hits bottom carb fine soon as I start it just revs up full any ideas thanks 

Ignition side crank seal is a possibility although I wouldn't expect the revs to go sky high instantly

Okay will try new seal thanks pal 

 Is the cable holder in the top of the slide missing, out of place letting the needle to move freely?

The rubber carby mount piece (between the carby and the reed cage) are known to crack and let air in

Will check these things thanks 

Spoiler

 

 

First off that is not the stock carb. That vent line, does it have a hole in the middle? If not cut iy in half, its not venting. Take the carb apart and blow contact cleaner threw that hole to verify.

Hi thanks for reply I did search the internet and said was stock carb ? I’ve cleaned the carb throttle nice responsive everything working good nice and clean now just unsure if there is ment to be screw in the hole with threads thanks 

Hi thanks for reply I did search the internet and said was stock carb ? I’ve cleaned the carb throttle nice responsive everything working good nice and clean now just unsure if there is ment to be screw in the hole with threads thanks and the vent line has hole cut

Happened to us when two events combined. That is, a faulty carb. float needle combined with the petrol tap being left on overnight. Fuel seeped into the crankcase causing immediate high revs when it started.

20 hours ago, Branny said:

Hi thanks for reply I did search the internet and said was stock carb ? I’ve cleaned the carb throttle nice responsive everything working good nice and clean now just unsure if there is ment to be screw in the hole with threads thanks and the vent line has hole cut

@Branny Beta OEM is usually a Mikuni carburettor. you cannot go wrong with blanking that hole on the VHST  carb you have fitted to your Beta  as it is only for use with bikes that have the exhaust mid box on the right hand side of the bike for example a GasGas.. just plug it with something . 

 I have given 4 suggestions. And you cannot even figure out its the wrong carb. Good luck, find a friend.

Only from experience, I would say it does sound like an air leak , which could be a crank seal or cracked inlet manifold (as  already mentioned)  or a gasket etc.

Although that carb may well not be original, if it's been running fine previously with that carb, then you don't necessarily need to change it for an original carb - just find out if it is a fault with the carb that can be repaired - like the missing blanking screw that has been suggested. 

If it is an air leak you are looking for, it  won't be massive, I once had a Yamaha that did the same , and the air leak was so tiny you wouldn't think it could have allowed enough air through to make it rev highly, but it did

Thank you all for reply’s will give it all good going through this weekend