I would think that the regulator is bad if it is a Nikki regulator take the top plug it has a nut with a Phillips screwdriver head in it remove it but drain down the propane system first and bont loose the o ring on the end of the plug. Install a pressure gauge it should get about 5psi with key on could go up a little on first key on but should come back to 4To ,5psi if past that the regulator is bad also it is possible that the main injector o ring is bad or broke on the end of the injector.if every thing checks out there are two popite valves in the throttle body housing that can stick of that is the case l would replace the housing hope this helps.