Was running fine, then shut off and smoked like...

Question

The heater had 3 gallons of fresh kerosene in it. It ran for about 15 minutes and then just shut off. It smoked like crazy as though it was spraying fuel on the hot baffle in the front.
I have two of them that are down this same way.
The other one would not start unless I took a heat gun and blew heat in the back end for a couple of minutes before trying to start it. It has been this way for some time. Weak spark? The spark looked good. The last time I ran it it ran for about 15 minutes and quit like the other one. Temp was down around zero. Possible water in kerosene??