The shims hold the needles further out of the main jet which allows a richer condition when they are actively 'in use'. The best chart I've seen to illustrate how the carbs work is this one:
(From
that page):
The air screw is most effective between idle through 1/8 throttle. The pilot (slow) jet is most effective between 1/8 through 1/4 throttle. The slide valve is most effective between 1/8 through 1/2 throttle. The jet needle is most effective between 1/4 through 3/4 throttle. The main jet is most effective between 3/4 through wide-open throttle.
Start with the 130s and see what happens. I'd still remove a shim though.
btw, are you not sure whether you have two shims per needle? I see your question (per needle?)
I believe that going from a 16 to an 18 is going to negatively affect your bottom end torque. It's an easily reversable mod, so try it and see what I mean.
