how to make your trail sled a mountain tamer

This past winter, American Snowmobiler's executive editor, Wade West, made the journey from St. Paul, Minnesota, to the mountains of Idaho and Wyoming.

In my conversations with Mr. Wild Wild West, prior to his western trek, we talked about riding in the thin air, and in the steep and deep. Here I pondered what is involved in prepping a '00 Polaris 500 XC for the mountains.

With this in mind, Performance Sports in Ashton, Idaho was scoped out to answer our questions. The small Polaris dealership owned by Mike Rasmussen, sits at Island Park's southern mouth. The boys here know the recipe that will make a sled breathe thin air, regardless if it is a short track or not.

Rasmussen has punched through the snowmobile industry for 28 years, crossed paths with all brands- some only a footnote in history- and has worked hard to make stock mountain sleds run with a bite. His shop also specializes in making short trackers emulate the long legged mountain goats.

OK, so a 500 XC is about to be towed from St. Paul, Minn., to Island Park's Mount Jefferson. What do you want to do to make the little twin run? Here are the basics from simple to more as laid out by Rasmussen.

1. Reduce main jet size.

For each 3000 foot change, according to Polaris' shop repair manual, drop the main jet at least four sizes. When snorkeling in the 7000-foot range, decrease main jet size by eight to nine sizes from a sea-level setting.

Generally, a two stroke motor loses three percent of its horsepower with every 1000 foot increase in elevation. To place this in perspective, a snowmobile running at 7000 feet will loose about 21 percent of its hp; that is 7 x 3 = 21. Other variables are included such as air temperature; the colder the air the more dense (rich) it is. Decreasing fuel flow is key to matching the reduced air flow.

In an another comparison, the little 500 XC, at sea level, will speed down a trail like a 700 RMK at 7000 feet. Now, you as reader, know why there is no replacement for displacement with mountain riders. Ask the big bore readers in the Rocky Mountain nose bleed section.
2. Lighten rotating clutch mass.

With the thin air, clutch engagement speed, rather the rpm level the primary clutch engages the drive belt, must be increased. Accomplish this by adding a heavier primary clutch spring and lighter weights. Engagement speed should hover around the 4200 rpm mark and up to 4800 rpm, the latter at the most extreme OEM spec level.

3. Tighten the secondary clutch spring by setting the driven spring into the middle position.

This improves back shift, thus allowing both clutches to quickly slam back down into the engine's grunt and torque.

4. Lower the gear ratio by dropping top sprocket size by one to two teeth.

When traveling through the deep snow and breaking up over a cornice, tall lake racing gears can't take advantage of an engine's torque. Hence, high track speed throughout the power band is paramount.

5. Drop the rear suspension.

By dropping the rear suspension, thus raising the tunnel, a snowmobile will plane through and on top the snow better. Additionally, the sled's hill climbing capabilities will improve.

If the snowmobile's rear most mounting bracket (also known as a suspension hanger) has a lower positioning hole, move the suspension down to it. Furthermore, the front most mounting bolts (next to the front drivers) should be lowered at least one hole - not two, if there are two. This may require some drilling; some tunnels have the holes pre-drilled, some don't. Generally, the front mounting bracket, placed on the tunnel's inside, has pre-drilled holes, but the tunnel may not on the outside. If this is the case, tap or punch the bracket's pre-drilled hole (to mark the hole's position) from the tunnel's underneath. Drill from the outside.

It must be stated here that if the rear suspension's front position is not lowered in conjunction with the rear mount, the track will tighten overly much. Rasmussen says it may be difficult to loosen the track enough to compensate for the dropped track at full compression.

6. Lengthen the rear suspension's limiter strap.

Strong and increased weight transfer is a must. Dropping the rear suspension will do little if weight transfer is not increased. Lengthen the strap at least one-to-three inches if you are riding in the deep powder. If mostly trail riding, leave the limiter strap in its original "St. Paul trail position."

7. Stiffen front suspension.
By increasing the front suspension's pre-load, winding the cam up to the middle position, the skis will stay firmly planted in the snow thus improving steering (and in the case of deep snow, rudder action). Additionally, the nose will raise quicker, hence allowing the snowmobile to plane quicker on the skis not on its belly pan.

8. Add a long-track kit.

Not really necessary, unless the owner/rider is planning on spending all their time in the west. A long track kit will smooth out the ride, but will change the snowmobile's handling characteristics.

For example, to long track our Polaris 500 XC requires some extra money and some patience. A long track will include rail extensions to lengthen the sliders to 136 inches. The tunnel will be stretched by adding a tunnel extension. A new bumper will replace the short track style bumper. The longer tunnel also makes for a great place to mount an external fuel rack.

The lug height on the 136-inch track will either be a 1 and 1/8 or 1.25. Changing out the front drivers will not be necessary.

9. Many times short track sleds, with proper setup and a deep lug track, burn the mountains and leave an unsuspecting powder sled wondering what short leg creature just mauled it up the hill. For flatlanders making the pioneer trek to the West, bring your sled, dial it up and have a good time.

For more information, contact Rasmussen at Performance Sports Inc., 208/652-7738