Propane burners and sooting

I have two propane burners that I use, a Darkstar and one from Bass Pro..... Both of them somewhat soot up the bottom of my kettle in a 60 min boil. Is t his the norm? I have adjusted the air inlet butterfly valve to get the bluest flame I can get, but still get some degree of soot on the bottom and a little up the sides of the kettle. Is this just what you get with propane? I use a butane hotplate to boil my starters in a stainless pot and get zero soot from it... It made me wonder if there is a propane burner that doesn't do that...

You should not have any soot. Are you brewing in the garage? Maybe there is too much of an air restriction.

I do brew in my garage, but only with the garage door all the way up, no air restriction there i wouldnt think.

sounds like the air mixture is off. what color is the flame?