[sho305]

The preload is two things, static and torsional. Static is spring pressure the spring has. Torsional is traditionally what is preload and the springs have a tang on the ends that lock into holes. Many aftermarket springs are for something else and do not have them so you can't preload them. If you get a umax they have them. Then you rotate (wind up) the sheave to the next ramp when you install it. The different holes will change the degrees you turn it to get to the ramp thus changing the pressure. The pressure is against the ramps causing them to shift down more with more pressure, this raises rpm. Static is spring pressure against the belt straight from the spring based on its size and the helix ramps have nothing to do with it. A G1 runs backwards in reverse and has ramps both ways for example, so you can't preload it, it runs more spring pressure with no preload. Most all 4 cycle carts run one way and can preload with the stock spring, in case of yamaha the HD umax spring also, aftermarket you are on your own. The umax was for carts with boxes factory or utility use to haul things etc. its longer and thicker wire.

With a ton of preload the stock spring can keep rpm very high, like WOT rpm all the time, though its not very nice to drive and there is not reason you need to go that far to get max power.

You can spacer a non tang spring but be careful of too much pressure on the sheave and you can lose top speed because the spring binds up.

Remember the static pressure on the spring is technically used for belt pressure so it does not slip, too much pressure wastes energy. The preload makes it not shift down to lower rpm so the rpm stay up with more preload but pressure is not changed a lot. The engine torque on the ramps is what increases belt pressure (clamping pressure) when under more power so it does not slip then. Aftermarket springs are a bandaid and that is why they are quite difficult to install and can in some cases even break cheap thin aftermarket sheaves, some of them are huge (some off ebay). That is why I recommend the umax and twist it up to what you need with preload.

You can turn your sheave down you ideally need a lathe, you cut the inside hub flat so they go closer together is all. The cut face is about 1/2" wide when complete. You can put the other sheave on it and fit a belt to see where you are at. Using a 1 1/4 wide belt on a yamaha can also do this somewhat but can drag more on the primary, but works, and is really nice on worn clutches. I have both wider belt (hd kevlar) and cut sheave. I think the sheave cut will help you the most as its the only thing that actually lowers gearing, then run the belt tight as you can get away with, it makes a big difference at <5mph speeds.

My HD wider belt and cut sheave the belt would stick out the top at rest about 3/16". As the belt wears it goes down some. Stock new belt sticks out less. The one sheave is metal and rounded edge so it can't stick out too much.