I've got a couple here for this project, not having any trouble whatsoever with the AC stick welder- anyway, I borrowed a 110V Lincoln SP125 for sheetmetal work. It's running .030 flux wire. Most of the work is done, of course on the last piece it started fawkin' up.
It seems to work OK for a few seconds then the arc will just die. Wire won't feed for a few seconds, but then voila it goes again. Almost like the machine will only run for 5 secs at a time. I've changed the tip, a few times.. lots of wire on the spool, liner feels really free like it should, steady feed when not welding... also it seems to sort of hunt around regardless of setting. It'll feel like not enough wire speed and sound funny, then a second later the wire'll be pushing me off the work.
Drive rolls are aligned- what the hell's up with this thing? I've only got 5 feet of bead to go, hopefully later today (Saturday)
Yes, I've played with speed, voltage- had it dialled for what I'm doing (16ga) and now this.

One of the diodes in the high voltage X former circuitry, on the 110 v Lincolns, is a fairly common failure, if used often for long durations.
Ive had 2 of them fail in the last couple of years on my Weldpak 125.
The symptoms, are short bursts of full power, then it will drop out of power, and the spool motor groans, like its trying to pull a train. It will get worse to the point that you cant even get enough power to stick the tip.
Repairs run about $100 or more. The second time it happened I just soldered in all new diodes, and replaced them all for under $20.
Also I find I can get better penetration, when I use .035 flux core, over the .030

Whats the duty cycle? 20? 10?

u checked ground is good I assume?

I dunno if flux core wire is bothered by wind or not eighter..

But the jumping around happened alot with me welding sheetmetal - with gas in wind..that and ground will bounce arc all over..

if none of these - my guess is the first responce here is right.

luck