Range leisure why does the flame burn black

Most likely cause is food on the burner or down inside the burner holes or possibly in the gas tube that feeds gas to your burner.

If it were mine Id take off the burner and gas feed tube going to it and clean them out with soap and water and get a small drill bit about the same size or a little smaller than the holes that are around the burner and push it through the holes by hand and rotate them by hand in the little holes and verify they are clean and unobstructed.If its a light weight burner like aluminum DO NOT Put the drill bit in a drill and drill the holes out, Some burners are so thin and cheep you could easily drill an extra unwanted hole in the back of the burner.If its a heavy duty cast iron burner you could use a drill if you are very carefull .there could possibly be greese or something inside the burner itself ,try to clean it out if possible.Some times insects like a small house spider will make a web or cacoon or something in there if you dont use it very often.

So after cleaning the burner ( inside and out) , and the gas tube,with soap and water, you dry it off with a clean cloth . If you have access to an air compressor with a blow tip, you would thoroughly blow out each hole on the burner ,and front and back of every other nook and crany or hole there is very thouroughly .After all that reasemble itand try it out. If thats not the problem then I dont know what it could be unless some how your gas supply is getting contaminated with something else before it gets to your stove . If this would be the case then all your gas burners will burn black. If it is only one burner that burns black then there has to be something wrong with that specific burner or gas supply tube going to the burner. Good luck with it ,Sincerely, Keith