low speed needle should not affect top end..open carb to full open and make sure the low speed needle is not entering the spray bar[start the engine and adjust top end.slowly close the carb.does it idle at all before stopping or die right away.if it dies right away,chances are the low end is to lean so back the low speed needle out 1/2 turn and repeat.if it idles for a bit then dies turn it in 1/2 turn and try again.may take awhile but really no other way to get the right setting.