Since 4 horsepower is converted to 2.94 kilowatts, they cannot match a 3 kW generator.
Your pump motor is 1100W. If it is three phase, a generator of not less than 2KW is sufficient if it is single phase, because the generators all have a three phase output, plus the generator; The power factor requires that the single-phase output power of the generator should not be less than 1.5 kW, which means that the total power of the generator should not be less than 4.5 kW.
I hope this helps!