The way I have been shown to sort the bottom end is to get it running at a fast tickover say about 3500rpm with about half a tank of fuel then hold the model nose up and with a long screwdriver adjust the bottom end until u get max revs then adjust the main needle whilst keeping the nose upwards doing it with half a tank means that when u fill it up it should run slightly rich and when nearly empty it shouldnt go to lean

regards goony