why does it trip 14amp breaker when i use skilsaw

Because our circuit breaker is a 13.5A and your using 14A, so it trips. Your going to need a more powerful generator. I just looked at the next size up a 6000 watts and they have a 20 amp at 120v. I used a WH6000 model as an example. By the way, I have the same problem.

There's a surge current associated with getting the blade started. The saw may only draw like 8 amps when it's running at full speed, but, on start-up it may draw 15 or 20 amps of in-rush current for the first second or so. This in-rush current is what trips the breaker.

Question for your question . How long is your extension cord & how old is the skill saw ? After running a skill saw on long extension cords for a long period of time ,It can burn up or deteriat the windings and may cause the saw to draw more amps .