By filing the end off the needle it is allowing the needle to come further away from the seat allowing fuel to flow. I'm wondering that if the clearance isn't great enough and the viton tip, swells a fraction that when the float sits against the carby body in the fully open position there is just not enough room for the needle to drop enough to allow the fuel to flow. I have just tried another one that I haven't started for some time and it won't start, fitted a filed needle and it still won't start. This is on an unmodified carby so I will pull that and see where I go from there. Problem I see with fitting a tap on the bottom of the carby the plastic is so thin there whatever I did it would have to be just glued on to the outside of the body but I will have a look at that idea. I have a couple carbies here that I have been unable to get to work for some unknown reason so trashing them is no problem
