It is no secret, your engine needs an air filter to keep abrasive dust, grit and water out of the combustion chamber. Most motorcycle use a pleated paper filter, and if these are neglected they can get clogged up. This means the engine has to work harder to draw air in.
A dirty filter can also affect the air/fuel mixture on carbureted motorcycle, making the engine run rich, wasting fuel and reducing peak power performance.
A new air-filter costs only a few hundred Baht, but blowing out the dirty one with compressed air is nearly free, and can take much of the dust and crud out. This will allow the engine to breathe easier and get more oxygen flowing, and that means more power!
Careless faring removal and refitting can mean misaligned ram-air intake tubes that cause air leaks and a loss of intake air pressure. Make sure the ducts are properly situated into the airbox, and any hoses or resonator chambers are correctly fitted. It's also worth cleaning out any leaves, insects or small rodents that may have gathered there. You'll be surprised At the things that can accumulate in these cozy conduits.