I removed the main jet extender on my mikuni and a brass sleeve fell out of the hole that that the extender was on. The brass sleeve has a thin tip on one end and is full size on the other. Which side do I push back up into the carb when re-installing.

Theres 2 rings or lips, The one that is flush with the end goes down ( by the jet) The other end has and extention past the ring/lip that goes up into the carbs throat ( the needle slides into it). If you look down the throat you shoud see it sticking up 3/16 to 1/4 of an inch. Not sure but I believe you can't go upside down with it because the jet extention will not beable to thread. could very well be wrong on that though.

Thanks. I dug around and found my book and it confirmed wut u said and wut I did.
Another question if u look back, how much difference will a 165 jet b from a 160, other than 5? I had a rpm increase when I let off the throttle just a little bit, so I'm thinking I was running a little lean.

That could be the case my boy. If you have the 165 try it can't hurt.
but a 162.5 might be the ticket.

It also maybe that your slide is set to far up causing the air entering the throat to expand then compress again right at the needle jet resulting in a flat spot at wot. When you let off the throttle a little the carb's slide is back at its optimum range and the air / fuel velocity increases.

A new set of plugs and a short run will help you see where your at.