Use only genuine Amal parts! Amal .105 needle jet. If you live at over 4000ft you really should be running these needle jets. Our years of experience here in the mile high city of Denver has shown us that .105 needle jets, #3 throttle slides, 180 main jets and a two ring I.D. needle work the best in most British twin carb twins including 650 and 750 Bonneville, Lightning and also Commando’s with the non cut spray tubes. Bigger main jet but same needle jet with #3.5 cutaways for single carb bikes.