It has been a long time since I converted gas engines to run on propane. The propane was delivered to the engine via the air intake system as a vaporized mixture. The carb became only a flow thru regulator via the throttle plate. There will be some mechanism for the propane vapor to be introduced to the air intake, perhaps by a vacuum switch. That will be the area to check for problems. Some systems had a primer that would allow an initial shot of propane vapor for startup and the vacuum would take over the flow needs after that.
