bubba931, step right back to the beginning, a submersable pump will draw varying amounts of current on starting. First check out the pump specifications, look for locked rotor amps, that is the current it will draw the instant the power is supplied.
Now gas generators have far better ability to start loads than inverters, given an overload that the pump in question would present it will dig it's heals in, the voltage will drop and ultimatly it will start (you stated that it did).
Cheep inverters have inherantly bad surge capabilities, usually less than 100% overload. Now a 1.8Kw pump will draw on start up 3-5 times run current(Kw), so to reliably start a 1.8 Kw motor you would need a 5.4-9 Kw surge capacity without soft start capability.
In my experience there is no way a 3Kw inverter, even one with 300% overload will start that pump because the overload is for a very few seconds, and submersable pumps can take 5 seconds to start on a good supply. Gas generators do not have these time restraints, as long as their thermal overload if fitted, does not activate.
I have glossed over the deep theory at this stage just to give you some idea of the problem, happy to expand if you desire.
allan down under
A life lived in fear is a life half lived.
