Get a generator rated about 50% MORE than rating on welder ... IF rating on welded on input supply line is something like 20 amp, get a generator capable of 30 amp out put (surge). Ever time you strike a arc the surge of current (though instantaneous) will be big, and if generator is to small it will "stall" every time you strike a arc and each brownout of power cant be good for internal electronics...
Find a welding web site (manufacturers) and ask question there to see what pros recommendation may be...
IF Hobart...
http://www.hobartwelders.com/weldtalk/
If Miller....
http://www.millerwelds.com/resources/co ... /forum.php
IF Harbor Freight ... Well you are out of luck....
Use Turboblues formula to find basics of "power " needed for welder...
The inverse of turboblue's formula is watts divided by voltage equals amperage (watts / volts = amps) ...
Usually a generator will say maybe 7000 watts (or whatever) surge and 5500 watts normal, but look at the plugs and circuit breakers for output, they will usually say 20 amp at 120 volts or 30 amp at 240 volts.... This is the telling factor...The big flashy numbers is overall output (surge) if not what actual output circuit rating is....
Dale