Putting last things together after full motor and tranny rebuild on '73 850 but had a problem with right cylinder/carb not running right. Did process of elimination (switched coils, plug wires, etc. has new wiring harness) and finally came down to the new Amal carb. Plug showed foul and muffler spitting, running rough and crapping out at 4k rpm. Now remember, brand new Amal carbs all set up for the 850. Pulled top off of the right carb and the needle out. Found that the needle circlip was in the wrong slot, resulting in way too of a rich mixture. This one was placed in a different slot than the left one which was correct. Boy, talk about an easy fix. One clue to carb problem was that when adjusting the right carb mixture screws it took a lot of turning to get any response from the carb at all. When needle put in correct slot, carb responded immediately to any little adjustment. That was a clue to watch out for when you are trying to tune your carbs. Bike now runs smooth, no cutting out and the plug looks perfect. Just one very little error can cause big running problems.