Fusion 900 Tech Tips
Stock clutching is garbage, pull it out completely this is what most of my research has led me to try and I have found to work the best.

Weights

Stocks are 10-74 which are way too light.
Switch to 10-78 or 10-80 weights to bring donw the revs.

Target rpm on the stock 900 engine is 7200-7300rpm.


Primary Springs.

Depending on what you want there are a lot of springs you can use.
You really have to watch high engagement carefully with the Fusions because of the torqure that the engine has and it's effect on the reverse system. If the engagemant is too high, what will happen is your secondary clutch will not lock into the reverse channel of the helix which will cause the secondary clutch to immediately open giving you no control over the sled in reverse, it will just try to keep moving.
I would suggest a spring with no more than a 150lb to 165lbs engagement pressure and no more than 310lbs full compressed pressure. Here is a list of springs.

Polaris

Dark Blue/White 120/310 (stock spring)
Black/White 140/320
Almond/Blue 150/310
Almond/Black 165/310
Almond/Red 165/310

The setup I current use is 80g EPI BellyBuster weights with an EPI Silver spring.

EPI

Black 145/280
Red 145/300 (recommended)
Silver 165/300 (recommended)

Secondary Clutching

The secondary clutch on the 05 models was off pretty bad aswell. The helix didn't have enough angle on it causeing the clutch to shift slowly fighting the primary which is trying to shift more quickly. It was a bad mis-match which cause the clutches to heat and eventually blowing the belts prematurley.
The 420719 Helix seems to be the magic helix for the 900's they have a steep angle on it and a shallow angle. The steep angle is a triple angle helix... 70-46-42 which works good for modded sleds or if you have you sled geared lower, and the shallow angle is 66-44-42 which is the recommended trck to run for a stock sled.
The secondary spring to use is a Team Red/Black or and other manufactures spring that has the same spring pressures... 140-240. The other problem with the secondary clutch was the spring binding causing excess friction in the clutch, this was remedied by using Derlin washers under the bottom spring cup and one on each end of the spring.

Gearing

Stock gearing is 25t top gear and a 37t bottom gear... this ratio is very high but it's ok to run if your an average sized rider or if you spend all day on the lakes. The most common thing to do is to gear it down a little. Research has shown that the 24/38 combo to be the best all around setup. You will lose a few miles per hour on the top speed runs but you will gain on the trails, belt life, and fuel mileage. You can also just put the 24t on the top, this also helps but gives a bit more dogleg in you chain.
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