Welding with CO2

I do a fair amount of welding at my shop, and until now, I've used CO2/Argon (75/25), TIG, and stick. The 75/25 works great and makes beautiful beads, but my bottles are the smaller 60 cubic foot size so they go fast and it's expensive to fill.

I picked up a larger K size bottle of CO2 for a great deal and started putting down some beads to learn the difference. The first welds were fine -- not as pretty as 75/25 but they had good penetration. Further on into the project, the arc started acting like I had a bad ground.....popping and wouldn't stay consistent. Double checked my ground clamp, good to go.

I looked at my gauges and increased from 10 CFH to 15. Seemed a little better, until the problem happened again. Increased from 15 to 18 CFH. Better, and then problems again. I look at the gauge again, and the needle is slowly increasing in flow. 30.....35....40 CFH. I watched it slowly go all the way around until it pegged the needle.

The gauges are CO2/Argon gauges that I used for 75/25.

Seems like something in the regulator is bad and I'm heading to the welding supply shop when they open, but I thought I'd ask if anyone here has experience with welding with CO2, and has had this happen before.