My club's Oil City-South Penn has a Burns made hot tube and chimney assembly. I believe a 6" tube. Heated bright orange at near the base to start, the burner is then throttled back to a mid to dull red for extended running. The high heat is used for bump starting - that is turning the engine against the compression stroke until the cylinder fires, thus starting the engine. We do not roll thru on starting! Starting is by hand only! I once saw a pair of men launched 10 feet into the air, trying to start an engine by standing on the spokes and rims. BAD idea!
One man was lucky - only bruised, the other not so much - he landed on an adjascent engine and ended up with a busted arm and a leg.
You tube video - NJAEMC oil city WMV. The hot tube is lit, main gas turned on, decompression valve opened. Once the tube is hot, the engine is rolled thru several times to prime the cylinder. You can hear the ignition right before I go to the front of the engine to shut off the decompression valve. The engine is then rocked against compression, and off it goes! After a minute or so, the burner flame is reduced. Thanks to Blace Flatt (club president) for the assist! I usually can start the OC-SP by myself, but I had hurt my back, and needed an assist. Thanks also to my son John, who took the video and posted it. Near the end of the video, you can see where we mounted a Tee with the decompression valve and a spark plug. We did not know how well the engine would run on the hot tube and propane, and were going to rig a wipe spark ignition system if the hot tube didn't work out. We never did set up the spark ignition! I love to hear the people ask how the engine runs without a wire on the spark plug!