Gosh some guys ruin them short shrift by intentionally sparking up on them
If the plant isn't running right just have a look.see everything at the return clamp is connected and tight
Bad ground is often an issue with mig not running quite as smoothly as it did
My recently changed clamp got damaged the other day and I am having to take greater care I get an adequate ground until I get out for a new one
A good ground on MIG is so so important. Make sure its clamped to a freshly ground surface and make surenthebcopper contactor's (if it hasnthem) are nice and shiny too by touching over with a disk.
My advice to anyone buying a hobby welder is always to ditch the clamp straight away and get a good one with a very strong spring and even better with copper pads.
I just helped a friend recommission a seriously neglected Clarke machine so that he could learn to weld, we changed the clamp before even trying.
I would advise this especially strongly for car body work where finding a place to clamp well is often difficult, it makes a lot of difference.
The better solution to that is to weld a tab of scrap to the car and clamp to that, with a good strong clamp with copper contacts, break the tab off later and dress the welds away.
That's what I do anyway.
The other thing mine has is a rectangle of scrap tacked to the back of the clamp for arcing on, when its a right mess I cut it off and weld another on, its always handy to have somewhere to arc up, even just to burn back a long stickout.