You answered your own question without realizing it. The Powermax cans have a clunk tube in them. If they are held upright you will be releasing liquid fuel. You did not say if you are connecting the powermax directly to the engine or filling an onboard tank. If you are starting the engine directly from the powermax bottle in an upright position you are introducing liquid propane/butane into the engine which will give you the way rich hot starts you are describing(as you are getting liquid,not vapor,gas directly into the combustion chamber.) Scott