Hi Danny, you can always try them nothing to loose, just a bit of time. The different colours are different lengths, you put the needle in the cap and put the float on and put it up to the light so you can check when the float is up the float doesn't hit on the body of the cap. When you look at it you will see what I mean. Then fit the cap to the carby body and see what happens, either stick up or flood out the primer bulb