So this started with the lift not starting. Had a tech in, offered a full tune-up for several grand--tech suspected the propane regulator needed to be replaced. Rebuilt the regulator. Replaced the fuel supply shut off solenoid. (Found bad seals in both.) The lift would now start, but would not run long and had developed a miss. Threw a timing light on the coil wire, and instead of a steady pulse the lift had intermittent fire. (also determined there is a delay from beginning to crank to the coil actually firing built in from toyota) Replaced the cap, rotor, and plugs.

Lift now starts and runs great for 5 to 10 minutes, enough time to warm up to operating temperature. Then the lift begins to miss, the miss becomes progressively worse and eventually it dies and will not start until it's cooled down. It's emitting foul sulfur smelling exhaust--unburned propane. I am stumped.