hello, my bike have to crank for long to start when cold. When hot starts ok. What can be the issue? Thanks

 

How many miles are on the bike? If you are closing in on 16-20,000, it may be tight valves...

 

Currently 22k miles, I just purchased this bike two days ago. When I was checking the bike before buying it started cold without problem. Now it needs cranking.

 

Tight valves, fuel system not priming, fuel system not holding pressure when off, old plugs, low battery, poor fuel......there are a million things that can cause it. Just asking such an open ended question without checking anything out first is a guessing game that won't help you. Start checking things, just like a car.

 

personally I would start with a load test on your battery. A battery can have plenty of voltage but not enough amperage to whip the engine over hard enough to fire right up.
Pretty much any automotive place (in my area anyway) will load test a battery for free.

But like mentioned above there can be MANY causes. gotta start somewhere though. If you need a new battery , check an amazon seller Capsmoto (something like that)
I just picked up a new one for my F4i , think it was like 40 bucks and works, fits great.