Hello, Just I purchased Yamaha FZs , my friend told that I should not go beyond the speed of 50kmph for first month . Is it true ?? Any technical reasons available for that argument ?

Hi, Your friend is very much right in saying so but instead of a month, it would certain kms. ( i am not sure, kindly check with your service center guys). This process of limiting bikes speed during the initial period is called 'Running in'.

Running in a bike is basically making sure your bike engines wears uniformly. Dont get scared! What I mean by engine wear is the piston properly bedding into the cylinder. So I shall now give a detailed guide as to how an engine should be run in.

Basically, during run in, your bike gets adjusted to your riding habits. Its sets up itself according to your throttle, braking, gear change speed, use of clutch, etc. So do not hesitate to whack in a little more fuel into your cylinder head if you are running as it is a required input for the bike to get used to you.

If you’re looking for fuel economy, dont raise it beyond 5 and a half 1000. Use the clutch smoothly, never let your engine rev by the force of the gear box. If possible, do a long run in. Go long distances during run in. Try maintaining the bike at about 3000 clicks for more than 20 to 25 kms at least! This will ensure that later your bike will give you a real solid mileage figure. Probably close to the company specifications. But keep one thing in mind, if you do such a run in, you will not be able to rip on your bike.

If you do so, you might face the following consequences:

Horrible mileage
Depressingly awful pick up and overall performance.
Reduced engine longevity and life.
Painful and irritating noises and rattles from your motor.
Things to keep in mind about economy run in:

Gear changes should be minimum.
Clutch release should be extremely smooth.
Engine should be at about 3000 rpm.
Higher gear should be used as often as possible.
Gear shift should be early.
The plus points of this run in are as follows :

Amazing mileage
Butter smooth engine and gear box.
Long engine life.
Less overheating of engine.
Tons of praises from your service guy!
Good resale value of your bike.

Your friend is correct. All bikes have to be run in before you can rip them. Look in your owner's manual in which you will find the manufacturer's recommended procedure for running in your bike optimally.