Personally I'd be very wary about 'changing-up' the fused plug rating.
To go with a 20amp fuse I'd want to be very sure that the supply circuit (wires in the wall) is capable of handling the potential total power being pulled.

Is it the 170 model or the 130 model?

The 130 amp version should be perfectly fine with a 10amp fuse.
The 170 am version should be fine with a 15amp fuse

Stewart what are to trying to weld ? Maybe you're just trying to pull too much power.

Try welding at a lower current and see if that helps.

Is you input voltage OK? If it's dropping below 200 that might cause problems too.

Be cautious with 'power-pulling' to avoid damage to supply circuits or even worse damage to the inverter circuits.