Thanks Emma,

the gears will change with or without the black pulley so am opting for removal of the black pulley and relying on the green pulley. I noticed with the black pulley it progressively bends the change line as you go through the gears. Took the trike round the block and the wide green pulley works fine going through the gears.

I checked the condition of the pulley and it looks good so fingers crossed it won't wear out. I might change it and put in a second guide derailleur.