Stezann-you're right, smaller machines have a lighter duty cycle. I believe mine is around 50%. Which in normal terms is 5minutes u can weld and a 5 minute break. When stick or tig welding you got to remember that after you burn a rod or a piece of filler wire, you stop, chip slag, move your piece being welded, clean up your weld and prepare for the next weld. Very rarely have I ever ran into having my machine duty cycle trip.
Poserman- I'm not sure what kind of Mig you were welding but it's the easiest of all the processes. I'd guess a 2 stroke exhaust was aluminum. Unless the Mig welder was setup for that, (spool gun) no wonder the weld broke. Welding is a lot more than grab whoever's welder and just weld whatever you've broke. Steel type, prep, process being used, gas, wire, filler wire, rods, tungsten, all that plays a part in what kind of weld you need to make.