hobart welding machine

[lexbec]

I have a Hobart mega arc 300G, 1984 model.It has a ford gas engine 2300, 4 cyl, 300 amps, 40 volts.
When I am welding with 1/8" welding rods, sometimes it will speed up and the heat will change, like I am burning a 1/4" rod. The only way I can get it to stop is to turn off the machine and let it cool down for awhile. Then when I start it back up, sometimes it will start out right, burning a 1/8" rod, but sometimes it doesnt and its like i am burning the 1/4" rod.
Also,, when the welding machine sits for a week or 2 , or during rainy weather, it will not weld. The only way I can get it to kick in, is to take my fingernail and flick the brushes. Most of the time it will start welding then.
Do you have any advice? Thanks

[Hobart Expert Dave]

If I remember right there is a exicter fuse located on the front left side of the welder. This is a one amp fuse for exicting the rotor. If this is blown it will only rely one the magnetics of the rotor as it turns over to exicte the unit for power. Now as for the current changing then it could be the brushes are loose causing this. As you said you have to sometimes play with the brushes to get an output.
Thanks
dave Evans