Terry wrote:
I have a lincoln Mig welder requiring 230V 20A single phase power. I
have a welding job to do where there is no power available. It has the
Nema 6-50P 3 prong style plug.

I have a coleman 5000W run / 6250W max generator that has a 120/240 20A
4 prong twist lock style receptacle Nema style L14-20R.

Is this 4 prong receptacle 3 phase power?
Very unlikely. That should be essentially the same as a 240 V home
power panel. 240 V with a neutral, so you have two 120 V circuits
and one 240 V circuit. The 4th prong is safety ground.
I purchased a 6-50 3 prong
receptacle, and L14-20 plug hoping to make some sort of adapter cable
so I could use my welder with the generator.

Is this possible with what I have? Can I just pull single phase 220
power from the X and Y out of the 4 prong plug (leaving the W
disconnected)? If not, is there a generator that has a 220V single
phase receptacle on it?
I'm not clear on the X Y W wiring. You should use a meter to verify
which terminals are the 240 V before wiring up the adaptor.
The safety ground should be pretty obvious, but on the twist lock
it is the prong with the flange.

This welder may be at the upper limit of the generator, and will
probably cause the engine to surge and dip a bit as the arc sputters.
If you are not maxing out the welder, it should work fine.

Jon