Trouble powering a deep well pump with a generator

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.
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Hi How about loading the gen set with that heater in series to 220V and measuring current with Amprobe to see if anything unusual? Tony
Tom wrote:

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I'm not understanding the problem. For either a submersible pump or 230 vac jet pump, both lines in the switch and (for a sub) to the well and down to the pump motor, are supposed to have 120 each. Together they make up 240. What am I missing?
Gary Quality Water Associates
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Did you wire the transfer panel for 240 to the pump , 2 legs bridged, is it getting 240 , did one leg blow a fuse giving it 120 , check voltage with gen and pump on.
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This is Turtle.
If you move a breaker in a box [ with seperate 240 breaker on two single breakers ] it will get two 120 volt legs with both on the same phase and you will not blow breaker with two leg stuck together at the pump. When the pump turns on you will have 120 volts on both legs but same phase and it will do nothing like this. I see this out in the country where home boys wire the system. It takes two seperate phases to make 240 volts.
I could be wrong here but it just smelled this a way.
TURTLE
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Did you check for 220 VAC at the generator when the well pump was doing its job?
Sure sounds like you have a loose or dirty connection. Time to check the wirenuts, and terminals.
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Christopher A. Young
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The gen has 2 legs each side 120, maybe one is bad but with a transfer panel you have maybe 4 fuses to your pump 2 on the transfer panel , one for each leg then your main box , one or 2 A loose wire, Fuse , or the gen.
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