fuel leaking, maybe burner is damaged. i had the same on 111T when i found hairline crack in the burner pipes that leaks only became hot on the running stove. absolutely invisible when it's cold.
It looks like you have a Primus "UFO cap" on your Radius "UFO burner" - I have learned by trial and error that this burner type is quite sensitive to flame pattern and dome height of the cap - less part of flames reaching the burner collar or slightly too low dome would cause that problem. If the flame turns blue when you lift the cap(long nose plier or two screwdrivers) a little, you have too low dome. If it turns blue at slightly less power but completely yellow at low power, it heats the burner to little and it may be corrected by attaching a windshield to the burner or enlarging some of the lower flame holes in the cap.
@Lennart F that is an early radius UFO cap, so a more rounded shape than the later model… effectively looks like the primus one but in this case it’s a radius original. Nicola
Try a new jet nipple in the burner first as it's the easiest option a worn one may be giving this problem as pre heating will give a blue flame until it cools slightly , a good heat & quench of the burner itself a few times & a soak in citric acid might help to clear any carbon build up. Stu.
I fired my Radius 17 to see how the flame pattern looked on my burner , my burner is slightly different to Kerophiles & the flamelets seem to impinge on the burner face as can be seen in the pics , hope this helps a bit. Stu.
my shmel-2 did that too. it's either the fuel to blame or a dosage problem,yellow flame means too much fuel.more fuel than oxygen to obtain a complete burn and a stoichiometric air-to-fuel ratio! disassemble, clean everything ,check every part for visible defects. gaskets too can be to blame. or start with fresh fuel AFTER cleaning and check
If only it were that simple! These 'special silent' burners are very close to the limits of practical workability, and are somewhat notorious for very hot caps in operation. If you read through previous discussions concerning these burners, it becomes apparent they a law unto themselves! I'd also argue that a proper decoke using heat and compressed air, if possible, is safer than the heat-andquench method (known to have cracked burners) and more effective to than ultrasonic.
heat and quench IS a "practice" when it comes to cleaning burner heads?! I quenched bearing steel 52100 in cold water from about 800 degrees Celcius and was expecting at least one blade to crack or warp... to heat a brass burner and throw it in cold water can only crack the brass... Better "forget about a burner" in a ultrasonic bath :-) than "quenching' them...
