
A variator is designed to adjust your rate of acceleration, at what RPM
your motor runs while it is accelerating and at what speed the motor is
revving when you reach the highest gear ratio available.
Now having said those things, the key is to have your motor
running at about 80008500 rpm's consistently while accelerating. This is
where your greatest horsepower is generated. If you are accelerating at
5000 rpm's or 9500 rpm's, this will decrease your acceleration because
your horsepower is not at it's peak.
Optimal performance is only achieved through trial and error. Changing your contra spring, and
then trying different roller weights is how this is achieved.
In order for you to understand which way you need to go with weights and
springs, you must first understand how the entire drive train works. 

Lets start with the front pulley of the variator. This is where your
roller weights and ramp plate are located.
Now as the
rpm's of the motor increase, the centrifugal force pushes the roller
weights out (Number 1 in picture).
The roller weights push out and onto the angle plates surface. This causes
the rear half of the pulley to move toward the front half of the pulley
(Number 2 in Picture).
When the rear half of the pulley pushes to the front pulley, it forces the
belt out to a higher gear ratio. (Number 3 in picture). 
If you are
thinking about getting a new variator, Let me first start by telling you
that it will probably not have any effect on your over all top speed. What
it will do is give you a more steady acceleration. The distance that the
rear half of the pulley can travel pretty much remains the same. Meaning
that it will only push the belt out as far as the stock variator will
which results in the same high gear ratio as the stock variator. The key
difference between the stock and performance variators is the angle on
which the roller weights travel and the angle on the angle plate in the
rear of the variator. This will only help give you a smoother, more
constant acceleration.
Now as for the different weights for the rollers. It is really rather
simple. The heavier the weight, the more force will be applied to the
angle plate forcing the rear pulley forward faster. If the roller weights
are too heavy, it will force the gear into too high of a gear too fast.
I like to use a 10 speed bicycle as a comparison. From a dead start, if
you are in 10th gear, it is very difficult to get going. But if you are in
first gear, it is very easy to get moving. the same principle applies
here. You want the weights to keep you in first gear, and as the rpm's
increase, it will gradually step the gears up until it reaches tenth
gear.
If your roller weights are too light, then there will not be enough force
to push the ramp plate out and the rear half forward. This will result in
good acceleration, but a low top end.
This is what the ratio looks like in low gear. You will see that the front
pulley is small, and the rear pulley is large. This is like first gear of
the 10 speed bike:
