prep your sled

AmSnow.com is now SnoWest.com

This past winter, American Snowmobiler's Mountain Team spent ample time on Cat's '07 model-year 800 and 1000 Crossfires and F-Series in the mountains of Idaho and Montana. Mark Boncher, our Senior Editor from our home base in Wisconsin's flatlands, spent time exploring the backcountry with us on the new sleds. We talked about riding in the thin air, and the steep-n-deep powder. We also discussed what's involved in prepping a crossover or trail sled for riding in the mountains, since more and more flatlanders are heading out here for our great snow.

Here are some simple guidelines for you Midwestern or Eastern riders that will help you prep your snowmobile to breathe thin air and tackle the steeps, regardless of whether you're riding a short-track or crossover sled.

Getting started
OK, so you're preparing to tow your sled from Minneapolis to the mountains of Wyoming. What do you have to do to make your 2-stroke twin run well? Here are the basics.

First, adjust for the air. If your snowmobile uses carburetors, reduce your main jet size; how much, is dependent on bore size, and elevation. For every 3,000 feet you go up in elevation, generally you should drop the main jet at least four sizes. So, when in the 7,000-foot range, decrease main jet size by eight to nine sizes from a sea-level setting. As a precaution, you should check with your dealer or read a shop manual before changing settings.

Generally speaking, a 2-stroke motor loses 3% of its horsepower with every 1,000-foot increase in elevation. So, a snowmobile running at 7,000 ft. will lose about 21% of its power. Another variable that affects performance in the mountains is air temperature. The colder the air, the more dense (rich) it is. Also, decreasing fuel flow - changing jet sizes to let less gas into the mix - is key to matching the reduced airflow because of thinner air in higher elevations.

To compare, an 800cc 2-stroke at 7,000 ft. will only run about as fast as a 600cc 2-stroke at sea level. You can see why us mountain boys say, "there's no replacement for displacement."

If you're lucky enough to have a sled that is electronic fuel injected, then generally nothing needs to be done to prepare the sled's fuel and oxygen mixing needs for the mountains. That said, always check with your dealer, as a different program may need to be plugged into the EFI's control module to prep it.

More mountain prepping
After jetting, you will need to lighten rotating clutch mass. With the thin air, clutch engagement speed (or the rpm level the primary clutch engages the drive belt) must be increased. To accomplish this, you must add a heavier primary clutch spring and lighter weights. For most 2-strokes, engagement speed should hover between 4,200 and 4,800 rpm, with the latter being at the most extreme manufacturer spec level.

Next, tighten the secondary clutch spring by setting the driven spring into the middle position. This improves back-shift, allowing both clutches to quickly move back in order to transfer power again if needed.

Additionally, you will have to lower the gear ratio by dropping top sprocket size by one or two teeth. This is important because when traveling through the deep snow, tall, flatlander, lake- racing gears can't take advantage of an engine's low-end torque. Powerful track speed throughout the powerband is needed in the mountains.

You may also have to lower the rear suspension. Dropping the rear suspension, in effect, raises the tunnel. A snowmobile will plane on top of the snow better this way. 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, which are next to the front drivers, should be lowered one hole (not two) if there are two. This may require some drilling as some tunnels have the holes pre-drilled and some don't. Generally, the front mounting bracket, placed on the tunnel's inside, has pre-drilled holes, but the tunnel may not have holes 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 underneath. Then drill in from the outside.

If the rear suspension's front position is not lowered in conjunction with the rear mount, the track will tighten too much, and it may be difficult to loosen the track enough to compensate for the dropped track at full compression. You also will have to lengthen the rear suspension's limiter strap because you will need the increased weight transfer in the mountains to get up on the snow and get the skis up. Dropping the rear suspension will do little if weight transfer is not increased. Lengthen the strap at least 1-3 inches if you are riding in deep powder. If mostly trail riding, leave the limiter strap in its original "Midwest trail" position.

Getting serious
You could also stiffen your front suspension. By increasing the front suspension's pre-load, winding the cam to a middle position, the skis will stay firmly planted in the snow, thus improving steering and in the case of deep snow, rudder action. Along with the increased transfer, the nose will raise faster, allowing the snowmobile to plane quicker on its skis, not on its belly pan.

Flatlanders who are serious about getting into the mountains can add a long-track kit to their sled. However, this is not recommended unless you're going to spend most of your time in deep powder. A long-track kit smooths out the ride and changes handling. It includes rail extensions to lengthen the sliders to your desired length.

You will need to stretch the tunnel too by adding a tunnel extension and a new bumper to replace the short-track style bumper. The longer tunnel also makes for a great place to mount an external fuel rack. The biggest expense that comes along with adding a long-track kit is purchasing a new track. If you're thinking of adding one of these kits, it may be cheaper to just sell your old machine and invest in a new crossover sled.

Let's ride
Many times short-track sleds, with the proper setup and a deep lug track, can burn up the mountains and leave an unsuspecting powder hound wondering what short-tracked machine just passed me on its way up the hill. For flatlanders making your pioneering trek out West, we say: Bring your sled, dial it up and have a ripping good time!

Remember though, before completing any of these mods, be sure to talk to your dealer, or contact a western dealer for additional advice on your individual model.