Yamaha Aerox YQ50 bogging down?!

Hi,

I have a yamaha aerox YQ50, when i bought it, it has a standard exhaust on it, a few weeks later the exhaust blew and i had it replaced for a Leo Vince TT.

Since then the bike has had a problem, when I slow down and get to around 5-10mph and accelerate again, the bike will bog down for about 20 seconds until it shoots off again, I have had the bike in the garage and the following had been checked:

> Clutch and variation has been stripped, cleaned and checked

> New rollers as the ones that came with my Leo Vince TT where not compatible with my bike

> Throttle and Carb had been tuned and cleaned

> The spark plug has been changed

The mechanic is running out of ideas of what it could be, just wondering if anyone has any ideas/ experiences of this? Its a lovely bike and wouldn't like to get rid of it.

Many thanks