Hi.
To start ensure that you have checked and replaced the air filter element. To replace the element you need to remove the fuel tank, then remove filter cover, held by three screws, and finally replace the filter, as in pictures below:
Filter cover:
If replacing air filter does not fix the problem, then you have to work on carburetor settings, first adjusting the throttle cable, then working on the carburettor synchronization.
The first part of the settings, adjusting the carburetor cable, is not a difficult operation, while synchronizing the carburettors requires experience and a good hear for the engine. I suggest to have this last operation done by a mechanic if necessary.
Here the whole procedure:
- Part 1 (throttle cable adjustment)
- Part 2 (synchronization A)
- Part 3 (Synch B).
Regards.