What I have seen in working on propane engines like these is over time the vaporizer, what you're calling a regulator, gets clogged up with a goo. I have no idea what it is, maybe something they add to propane to lubricate propane pumps, buts it makes a mess of inside of vaporizer. I have tried to rebuild vaporizers with mixed good/bad results, to the point I finally gave up on that, hard to charge a customer for a vaporizer rebuild that don't work, and instead fitted a new vaporizer. One thing you must do if you do that is get the correct vaporizer for the engine as they use different springs inside for different engine applications. Would be best to call Clark for correct unit.
As for the propane carb, if it has something like an Impco model 100, you can remove carb, disassemble, and clean with carb cleaner, then replace diaphram.