The Lincoln 140 family — the Weld-Pak 140 HD (K2514, K5365) and the Pro-MIG 140 (K2480) — all run the Magnum 100L gun, so they share the same feed path and the same failure points. When wire won't feed, it's almost always something in that gun, not the machine. Below are the causes that come up most on Lincoln owner threads, in order of likelihood, each with the specific Magnum 100L part where one is involved. Verify your gun's code (K530 family) before ordering, since longer guns take a longer liner.
Unlatch the tension arm off the drive roll and pull the trigger. If the drive roll now spins freely, the wire is jammed downstream — and on the Magnum 100L that is almost always the tip. Pull the tip and sight the bore: oval or arc-marked means replace.
Fit a fresh Magnum 100L tip sized to your wire — Lincoln KP11-35 for .035, KP11-30 for .030 (the tapered KP11T-35 is the same size in the longer body). Tips are a couple of dollars each; keep a strip of spares, since a worn tip is the single most frequent cause of a Lincoln 140 that suddenly won't feed.
Open the side panel and look at the drive roll and the two pointed wire-guide nodes on either side of it. Packed-in debris, shavings, or glaze there restricts the wire even when tension looks right.
An owner who fought intermittent feed traced it to those two guide nodes being gummed up: loosen the small retaining screw, lift them out, clean them and the roll groove with brake cleaner and a straightened paperclip, and refit. Clear the inlet guide while you're in there.
Disengage the drive roll and hand-pull the wire through the gun. Heavy, gritty drag (rather than light, steady pull) is the liner. Don't compensate by cranking roll pressure — that just shaves more debris into it.
Blow the liner out; if it's kinked or fouled, replace it. The Lincoln KP1937-3 liner fits the Magnum 100L (K530 family), feeds .025–.035 wire, and ships as a 15 ft length you cut to your gun's length. Cut it square and to the right length — long or short both feed poorly.
Rolls turn but wire stalls (slipping = too loose), or wire piles into a birdnest at the inlet. Check which side of the roll faces the wire.
Set tension by the half-turn-past-slip method (back off, feed against scrap, tighten just past slipping). The 140's drive roll is double-sided and marked for two wire sizes — run the side stamped for your wire, and flip to a knurled roll for flux-cored wire.
Unspool a foot and look for surface rust — common on a partial spool left on the machine in a humid garage.
Cut back to bright wire; replace the spool if the surface is rusted through. Store partial spools sealed with desiccant. Rusty wire binds the liner and tip and mimics every other feed fault.