Could it be unburnt propane in the exhaust? A loose/bad gasket between the carb and the engine intake?
With everything off get out the trusty soapy water and wet down every junction and fitting. If no leaks prior to the engine then it is exhaust or in the intake area.
Make sure your LP/CO detector is in good order! And good luck!
2017 SLX 195RB
2021 Jeep Grand Cherokee Summit L 5.7L V8
Andersen WDH hitch, Renogy 100 AH Lithium &
200 Watts solar panels from Renogy
Prev. '14 Jeep Grand Cherokee Overland, gas 3.6 V6