I own a yamaha gladiator ss 125cc bike. done just 3000km on it. if i decelerate, shift down then try to rapidly accelerate again i get sudden jerks from the bike...this problem is intermittent and doesn't happen everytime..also sometimes i get a random high frequency sound from the engine which doesn't last for long but appears every now and then.... i think the problem may be due to valve clearances....please comment...**** yamaha service centers are unable to solve my problem

in a standard carb when you twist the throttle you directly control the slide, while in a constant velocity carb the throttle opens and closes a plate on the engine side of the carb, and based on the vacuum created by the piston the slide raises up, keeping the velocity in the carb constant.
And most street bikes come with factory carb settings that have been set to meet all the pollution regulation laws, but it is very easy to adjust these settings to get a bit more out of the bike, dont understand why your mechanic wouldnt work on it... hope that helps with the carb quistion.
but not quite sure about the noise, maybe its the crankcase breather, but it could just be a normal feature of the bike, not really able to tell without hearing it. in a standard carb when you twist the throttle you directly control the slide, while in a constant velocity carb the throttle opens and closes a plate on the engine side of the carb, and based on the vacuum created by the piston the slide raises up, keeping the velocity in the carb constant.
And most street bikes come with factory carb settings that have been set to meet all the pollution regulation laws, but it is very easy to adjust these settings to get a bit more out of the bike, dont understand why your mechanic wouldnt work on it... hope that helps with the carb quistion.
but not quite sure about the noise, maybe its the crankcase breather, but it could just be a normal feature of the bike, not really able to tell without hearing it.