Excerpt from a Technical Bulletin:
The Forney 140 MIG as well as other high output 120V machines often produce end-user frustration due to the breaker popping and needing to be reset. This is a common problem and is very noticeable if the customer is using a 15 Amp breaker, using .035” wire, or is pushing the wire feed limits of the machine while on tap setting 4.
When designing a 120V machine, there is a balance between maximizing the output of the machine or never blowing a breaker, but having a poor output machine. We chose to maximize the output of the machine as the machine settings can always be turned down. The performance of the Forney 140 MIG machine has the highest rated duty cycle and output at 90A at 35% in its class.
Try reducing the tap setting, reduce the wire feed speed, reduce the wire diameter, or get a less capable machine. Also, verify the breaker output and have an electrician install the largest breaker that can safely be used per electrical codes. The chart below will provide some guidance: