Engines that run on LP can flood, the way that Gasoline Engines can flood.

In regard to the LP Vaporizer/Converter, the Diaphragm might look OK, but sometimes it can develop a pin hole leak that is very difficult to see.
You might need to rebuild or replace the Vaporizer/Converter.
Lots of people that own LP forklifts take for granted that their LP tank works fine and the gauge on the tank might be defective. You might want to buy or trade in, if you can, the LP tank.
Pull the Spark Plugs and Distributor Cap and Rotor. Take a good look at them and replace them AND the Ignition Wires at the same time, if necessary.