what causes a bike not start on the first button push? sometimes I have to open the choke or give it a little gas.

 

It's called "real life", and is no cause for alarm.

Getting an engine spinning from a dead stop is actually quite tricky and handled by some vary cleverly designed components in the fuel system. Often the engine needs a slightly richer overall mixture to fire when cold so as to achieve a combustible fuel air mixture where the spark is at the spark plug. Other times the mixture might be a little too rich and requires more air. Either way the engine is better regulated once it's actually running.