Bogs down when accelerating and lean surging

[ckahleer]

Bike starts and idles fine, but bogs down just off idle to 1/4 turn. Give throttle a good crank and bike accelerates fine. Also lean surge when gentle riding 35 - 55 mph.
Shimming the needle .050" helps, and shimming to .080" is almost acceptable. I'm considering shimming to .100", but would like some input from the group as to why I need to shim at all.
Carburetors, air box, exhaust is all stock. New air cleaner, Replaced needles and needle jets but that did not help. Fuel level checked with clear hose. Slides seem to raise and lower normally with carbs on bench connected to shop vac.
What am I over looking?

 

[grizld1]

What carbs, what ignition, are pilot jets clear and correct series, have you checked for vacuum leaks at throttle shaft ends and carb boots, are new needle jets and needles correct genuine Mikuni or repop?

 

[XSLeo]

If I was you I'd follow grizld1's advice, he knows carbs.
Leo