During power outages I backpower my house through a transfer switch with a 4000 watt (5000 watt surge) Coleman generator. In the past, the generator has easily powered the refrigerator, furnace, well pump etc. just fine. During the last power failure I was experiencing slow recovery on my water pressure and I found that when the well pump kicked on, the voltage dropped from 220 v to 110 v in the wires feeding the pump. The pump is 220 v, 3/4 HP, 7.0 amp, two wire feed. Once the grid power is restored the pump works great, so I suspect my generator is malfunctioning.
I have tested the generator by plugging in two 1800 watt heaters to the 110 v outlet on the generator and measuring the voltage at the 220 v outlet, which remains at 220v.
By the way I did turn off all the house circuit breakers except the pump as a diagnosis during the power outage in case I had left some high wattage appliance on - no change.
Any idea what might be causing the issue? Thanks in advance.