My job involves maintaining a large fleet of equipment and out of five guys me and one other do most of about 200 forklifts. He has a drivablity issue going on with one right now. A otherwise good running CAT with a 4 cyl LP engine (which is actually dual fuel, gasoline or LP). It runs excellent until under load then dies out. We have the luxury of having many of the same kind so he switched out known good parts. Hers what he's tried-either new or known good swap: Distributor, HEI coil, carb/governor, LP vaporizer, plugs-wires, r & r intake and checked for issues, compression-all 150psi, timing set right, all fluids good. These units use the gas carb as a LP carb when in LP MODE since you basically only need a butterfly and governor, so he even switched it to gasoline mode and it still did the same thing. For you forklift guys its a Pugeot engine with a Impco model J vaporizer. It started out as a probable tune up and has grown into a real nightmare. He just asked me to help today. Oh, and to keep on topic we do have a few tractors in the fleet.