Acetylene regulator sputter

Two ideas. The first is that you're drawing too much acetylene too fast, and are getting acetone drops in your gas stream. This is bad news. Remember, you can only draw 1/7th the tank capacity.
The other idea is that your regulator needs servicing. If your diaphragm is sticking, it can start bouncing like that. If your regulator is made by an offbrand or import manufacturer, this is the first thing to suspect. Most Harbor Freight Victor torch kit clone regulators have sticky diaphragms. They can be repaired, need to take them to a good regulator repair guy. If your town doesn't have one, send them here, because Seattle has a real good one:
Hansen & Miller 4101 Leary Way NW Seattle, WA 98107 206-782-8842 No email, no Web page, not cheap, excellent technicians, best around.
Grant Erwin Seattle, Washington