Yes there is the puff.. The can is also sucking in air to replace the fuel going in the tank also as I pump the fuel... I am not sure it is the nitro cooking off... But am certain something is ... What I do know is that halfway (two to three days) through the can the engines start running like they do with low/no nitro fuel which I have tried but that's another story.. A fresh/cool can of fuel cures most of the problem... The old can never becomes usable in the 4 strokes even when cool... Perhaps it is the alcohol "burning" off. I don't know.. But something is gone... I have never knowingly seen an engine run with no alcohol in the fuel... Hopefully I will get a response from the manufacturer with some info on fuel and high temps...