Ok.....
I'm glad RedRocket linked you that video, I forgot about it and;
That video is probably the best visual for those starting to think about c.v.t. mods as it let's you get an idea of how the different parts work as a system that seems to float smoothly thus the term automatic.
For some reason most new to this system refer to it as a clutching system, and this seems to confuse people and get them thinking there is something slipping normally.
In truth we are working on two pulleys that are in two pieces with each half called a sheave. Splitting the pulleys allows for the variable distance between the sheave faces the belt rides on and this might be what generates the comparison thinking to an automatic gear shifting system we use in other vehicles.
Both pulleys are bolted in place on a shaft with a spring on the secondary (rear) shaft separating each sheave, with a nut retaining the sheaves of both pulleys on each shaft. As the belt does not stretch, the squish tension forcing the secondary sheaves together makes the belt want to ride high on the secondary pulley thus forcing (pulling) the belt deep into the primary pulley.
At zero ground speed with the pulleys not turning, the primary sheaves are spread to their widest distance gap allowed and the secondary sheaves are squish closed to their narrowest distance gap then;
Once the primary pulley starts to turn the side force squish tension of the secondary spring keeps the belt from slipping, keeping the belt tight in the primary to transfer power to the secondary pulley hooked to the transmission.
As ground speed (wheel spin rate) increases the secondary spins faster from an increase in the rotational spin rate of the primary pulley as the engine r.p.m.'s increase, and this rotational force causes the weights inside the movable primary sheave to slide outward, toward the outer edge of the weight channels, being rubbed against the cam-plate bolted to the primary shaft with a wet-clutch on the other end. The only clutch in this Yamaha drive system is lubricated with engine oil, and the c.v.t. pulleys are not.
Remember a rock on the end of a string, the fast you can get it spinning around your head the further the rock gets away from the center of axis (the other end of the string).
As all stock dimension Yamaha weights are the same diameter when new, only the weight of the weights vary, at rest simply changing the weight of the weights does not change the pulley ratio in the system, so there is no difference in low end pull from zero ground speed; but once the pulley system starts to turn heavier weights will start to move against the cam-plate at lower engine r.p.m.'s and lighter weights will take more engine r.p.m.'s to start the weights moving. This is correct when using the same spring with both weight sets, changing the secondary spring changes how the weights move, and for this reason remember when doing c.v.t. mods always do one mod at a time to learn what that part of the system does.
Now here's the deal; we are not modifying the engine/air pump for more power, we are relying on drive-line system modifications to magnify the stock engine power produced. We are changing internally lubricated parts, we are changing parts outside the engine.
Engine builders know from physics torque can be multiplied/magnified and horse power cannot be magnified. That's why N.H.R.A. top fuel cars take off at very high engine r.p.m.'s and let a computer controlled clutch pack slip. These car chiefs rely on the horse power curve to drive the car which is the exact opposite of what we do with the Yamaha grizzly drive line.
We rely on the low engine r.p.m. torque to drive the machine, and to get more feel good in your butt dyno we raise the pulley ration by increasing the distance between the primary sheaves at the lowest engine r.p.m.'s as the wet-clutch shoes start to engage the primary shaft drum.
This can be done with shims or machining or like I did, by reducing the actual diameter of a set of weight covers.....anything to cause a greater distance between the primary sheave faces. If you only do the weights you're trying to sling the weights with stock non-magnified torque, so when you find the system reacts sluggishly you'll know why. This is also the type of result from installing taller tires which reduces the low end pull feel of a grizzly. The taller tires change the gearing ratio of the drive system and make the machine sluggish. On a side note, if you install 11% taller tires, raising the pulley 11% will restore the stock low end performance feel with the taller tires installed. If you can raise the ratio more than that 11%, the grizzly will feel better than stock.
As you do more and ratio gets bigger eventually you max out the ratio for the best increase in low end pull from a stock air pump configuration. This is extremely important for those wanting to go further with additional c.v.t. mods, to stay away from internal engine/air pump mods, for other benefits like lower engine r.p.m.'s when cruising to generate much higher m.p.g. for greater distance covered on a tank of gas, or maybe higher ground speed than stock.
As for how Yamaha markets their products, most pitchmen make $hit up to sell what they have, and as I've never seen anything from Yamaha's engineering department on a supposed gearing difference or whatever, I feel the Kodi is more a bargain basement offering for those willing to take less to pay less. I have read posts that the difference in size between the knees was a deciding factor, OK....but I have had riders on my 660 that were just over 5' tall and they didn't have a problem with the size, and wouldn't come back to camp until the low fuel bar started to flash. There is an ass for every seat, get what you want.
If you want to try different mods to your system, knock your lights out but keep the old parts if you make a mistake so you can get the system back to stock. Back in the day I had to go back to stock a few times to figure out why the mod results didn't match my goal.
Let us know how deep you want to get into c.v.t. mods.
