I hate that everybody calls the vaporizer a "mixer" The vaporizer is NOT the mixer. It is a diaphragm operated device that controls fuel flow based on vacuum, and the engine coolant runs through it, in order to heat up the liquid propane and turn it into vapor...hence the name VAPORIZER! It also regulates the fuel flow down to a much lower psi before it enters the carb.
The correct reference for "mixer" is actually the propane carburator itself, that's mounted to the throttlebody. They do two totally different things. Actually all carbs are "mixers" for that matter, as they all mix some form of fuel with air.
Since it does not have a VAPORIZER, and only has a liquid propane line running straight to the carb, it's not vaporizing the propane before it enters the combustion chambers and I would assume most engines usually don't have the compression to combust straight liquid propane and run smoothly. My propane engine always seems cold natured until it warms up, when the engine warms up, the propane begins to vaporize as it passes over the heating fins inside the vaporizer that are heated by the engines coolant. Plus it would be an unregulated fuel flow into the carb, since the vaporizer also regulates that too. Also, fuel and air mixture is something else.
I think you are chasing your own ass troubleshooting this without a vaporizer.