I have 6000w generator, and I'm getting a little bit of power form it but not the same that a got form my friends 5500w. What could be causing it not to have enough power?

Are both units running at the same/correct rpms?

Most generators have two settings on them one is the start up setting the other is the gov setting or the load setting. Check your voltage at start up. Increase you idle adjustment if needed. Then plug in something that will pull a load and then adjust gov setting to the proper speed to maintain proper voltage.

Hi,
Some generators have an idle-down feature when no power is drawn. If this is present you must "load" the machine to rev it up and check then.
Some generator ar brushless and some have brushes. One with brushes is less expensive to manufacture but a brush can stick, often in a heat-damaged brush holder.
A brushless version uses a bridge rectifier to provide the power to the receptacles and to the generator field that in turn creates that power. So in essence the generator extracts a small amount of potential to enable it to create a greater amount of power. Damge to thid circuitry would be suspect in this case.
Peace,
Clarke

With respect, it sounds as though the rectifyer is faulty in the alternater that generates the power,this is a part you can replace yourself, write down the make and model number and go online for the replacement part, good luck, honestwelsh