I have an SIP gasses Handymate .. bought secondhand.
What is the input current, (amperage), draw of the unit? Is the outlet wiring that it is plugged into of sufficient size to supply full power to the unit? For example, if you are in the U.S. and the unit runs on 120 volts, if it draws say, 18 amps but your outlet is wired with 14 gauge wire, The voltage drop under the load of welding, which is nothing more than a dead short, might be below the minimum, operating voltage of the wire feed motor. If my guesses of these values are close or correct, an outlet wired with even 12 gauge wire would be close to the edge of it's limits. If it were my setup, I would have a dedicated outlet wired with at least 10 gauge wire which, at a reasonable length, is good for up to 30 amps. If the outlet that this is plugged into has 2 outlets, plug an AC volt meter that is set to something above your local power into the second outlet at the same location, 120 or 240 VAC. Then weld something while someone watches the meter. If it is 120 volts but drops to 100 or 90 volts or if it's 240 volts but drops to 200 or 190, then your supply wire is too small. Think of it as trying to feed a garden hose with a fire hydrant. This condition will not necessarily blow your circuit breaker either. If it is fused at 15 or 20 amps, 1) You aren't welding long enough to build enough heat to pop the breaker and 2) if this outlet is a fair distance from the fuse / breaker box, it would be a good bet that a lot of the heat needed to pop the breaker is being built up inside the wall in the wire's resistance rather than at the breaker where it is needed. Good luck.