I am a forklift mechanic here in the U.S and all of our forlifts run on propane . We have only one A-15 in the hole fleet of 120. This perticular lift can run on propane or gasoline by the flip of a switch. We have to crank it on gas , then flip the switch to propane cause it doesn't like cold weather.What kinda fuel lock & convertor are you using sleeper? The black stuff that gets cloged up in the fuel lock & convertor is actually has an oil base , we have the same prob.If you ever tear down one of these engines after a few years or so there is alot of carbon buildup. in the intake & on top of the pistons too.