One quick thing to try. Make sure that you are not clamping down hard on the bolts that secure the torch head into the red torch mount. Really ease up on these so that they are barely tight. We have found this can cause intermittment firing.
Also cycle your electrode spring up and down and make sure your consumables don’t have any soot on them; if so clean them off. It’s also a good idea to make sure that your retaining cap on the torch is not very tight either just barely cinch this down.