Welder amps?

When using welders especially stick try to use it as close as possible to the fixed power source. The time of day that you are welding can be critical as well depending on where you live and how stable your power supply is. Recommend using an independent power supply for your welder (generator). With a 200 amp welder 22amp circuit I would use nothing under 7kva. I have often switched to my portable Genset for better welding results. I hope this helps you out.

never run an electrical wielder on an extension cord !you will ruin it or melt the cord !

When the welder is running the voltage will drop to zero and the amps will raise to max.

The core size of the supply cable could be too small. Is the cable becoming warm under load? If so, then replace it with a cable that has a larger core size E.G 2,5 cubic-square m/m per core or greater.

Welding unites have a core saturation time called -intermittent- as the coil warms up the coil resistance increases and the amps fall. Your welding unit could be too under dimensioned for the job in hand.   

You check the voltage and it's still 240, but under load there's such a thing as voltage sag, and you're not testing under load.  Chances are very good that at heavy amps you're not getting anything like the full 240.

  You need a thicker cord, a shorter one, or both.

the voltage might say 240 volts but under load the current is dropping because of the long extension lead 

More then likely the extension cord needs a larger wire size in order to allow the proper flow. Most extension cords tend to use the minimum sized wires they can get away with. Look, if possible at the gauge your extension cord uses and then find ones that can carry more.

The problem is most likely due to the length, and possibly the conductor sizes, of the extension cord. All wiring has a resistance which can cause a voltage drop when under load, including the house wiring. The higher the load the more the drop. Even a 5% voltage drop will give a notably reduced performance of the welder when welding. To get a true idea of the voltages you will need to get someone to check the voltage at the supply outlet / socket and the welder end of the extension cord while you are trying to weld, your multi-meter will do to check this, and if the voltage is considerably lower at the welder end of the cord  you may need to to use a larger capacity of cord or use the welder closer to the supply outlet / socket.

Hope this helps.

support page at the maker's website

Did you check the voltage while the welder was producing the maximum amps?