Charley notes:

Are you getting low on propane? When getting near the end of the available
propane in a tank the chemical that they add to propane to give it a
distinct smell will be burning off at a higher than usual rate and will
produce a very offensive odor. Try switching to a full tank before you spend
rebuild money on your heater.

It was low on propane, but the stink started hours before. When I turned the
head upside down to check the numbers, I found that the screen had pulled away
almost all across the head.

I'll spend money for the screen. If it takes more than that to fix it, I'll
find another route, something on the order of finally hooking up the thermostat
on my shop furnace. Right now, I don't want to spend the time it needs figuring
out the 2 wires (thermostat) into the 8 terminals (furnace) bit. Next week, a
guy I know who owns an HVAC outfit can tell me which is which.

Charlie Self
"Vote: the instrument and symbol of a freeman's power to make a fool of himself
and a wreck of his country." Ambrose Bierce