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120cc Snowmobile Basic Setup

Bypass the Governor

The Quick Temporary Bypass: There are a few quick ways to do this, but they should be
only used as a 'short term' option. The quick bypass is to use two zip ties and disable the
governor spring by compressing the spring with the zip ties so it can't stretch. To do this,
locate the governor spring by watching the throttle linkage on the engine and press and
release the throttle several times. Watch the linkage to locate the spring that stretches
and retracts with each push of the throttle. You might need to hold the governor lever
(long lever that comes up from the crankcase) still while doing this to see the correct
spring. Once you locate the spring, place two zip ties on the spring. This should now make
the spring act as a rod and thus disable the governor. Make sure your snowmobile is
securely on a stand and test it before starting it on the ground.

The Correct Bypass: The correct bypass is to remove the governor gear from the
crankcase. This is especially important on the Arctic Cat Sukuki engines because they
tend to shatter under the addition rpm. To do this, you must first loosen the engine from
the chassis. You can sometimes pull the engine part way up and then tilt it at a 45° angle
just so you can remove the side cover. Once it's either tilted or on the bench, remove as
much oil from the crankcase as needed to remove the side cover. Remove the side cover
and bring the cover to your bench. On the inside of the cover you'll find a small plastic
gear with some weights on it. Put rubber, folded cardboard, shop rag, or some other
protective material on top of the gasket surface so it's not damaged. With one hand
supporting the gear, use a screwdriver with the other and slowly pry the plastic gear off
the mounting shaft it's on. Now replace the cover to the crankcase and replace the engine
into the chassis. Now you'll want to replace the governor spring with a rigid linkage rod.
You can use different types of material for the rod, but thanks to my father's suggestion
I found that the rod on a utility flag works the best. It's the correct diameter wire and
it's very stiff. It works perfect!! Thanks Dad!

Upgrade the Valve Springs

You'll want to give your engine an adrenaline boost by replacing the OEM valve springs with
a set of super charged valve springs. Valve springs have been the most controversial topic
from 2005 until 2011 in which I've lead the charge, and it's now a well-known fact that I
offer the best valve springs available today. Our 5th generation valve springs are made
from a special metal, are designed and built as close to specification as possible without
exceeding it, and have been tested and passed by every club that does testing as of spring
2013. I offer valve springs for both Arctic Cat and Polaris.

To change the valve springs you'll first need to remove the valve cover. Before you begin
you'll also need to remove the rocker arms and put pressure on the valves from inside the
cylinder. To remove the rocker arms just remove the locking nut and then unscrew the
rocker pivot nut/bolt. You can put pressure on the valves if you have a cylinder
pressurizer, which most of us do not have. You can also use about 5' of ¼" rope, a small
screw driver, and a vise-grip. You'll need to watch in the cylinder through the sparkplug
hole until you see the piston approaching top-dead-center. Stop about 1" before the top
of the stroke. Now carefully feed the ¼" rope into the cylinder until it's fairly full. Now
continue to turn the crankshaft until the piston is firmly pushing the rope against the
valves from within the cylinder. Now you can use the vise-grip and lock it on the clutch
collar and against the belly pan to hold the piston against the rope. By doing all of this,
you won't have your valves drop into the cylinder when you remove the collets (keepers).
You'll then need to remove the valve spring retainers, collets (keepers), and valve springs.
Put the new springs in and replace the retainers and collets (keepers).

This does sound easy, but it's not the first few times. Doing one valve spring at a time
might be better the first time or two. You'll also need to make sure the collets are set
properly in the retainer. If it's not all the way in they can pop out, and if they are too
deep they can cause the valve springs to bind. In either case, the results are not good.
Now that you have the new valve springs in, you need to adjust the valve gap. This is the
gap between the top of the valve stem and the rocker arm. First reinstall the rocker arms
and barely snug them up. You'll need a feeler gauge to set the gap to .004". Rotate the
crankshaft until one valve opens (rocker arm pushes the valve down). Now you're ready to
set the other valve. Place the feeler gauge between the valve stem and rocker and tighten
the rocker arm lock nut. Move the feeler gauge and you should feel contact between the
two surfaces, but it should be fairly loose. If it's not, then loosen the lock nut, turn the
pivot nut/bolt slightly, and retighten. Check the gap again. Repeat this until the feeler
gauge is snug but moves easily between the surfaces. Now repeat for the other side by
first turning the crankshaft again until the other valve opens. Now set the remaining valve
gap.

Adjustable Main Jet

Adjustable main jets are a huge benefit in a few different ways. Since carburetors are
sensitive to temperature and air density changes, you want to be able to quickly change
your carburetor settings between heat races, especially as the sun comes up or goes down.
These environmental changes can significantly affect your engine performance. To make
these changes quick and simple you can install what's referred to as an "adjustable main
jet". This is a part the replaces the static main jet that's located in the bottom of your
carburetor and allows you to adjust how much fuel is allowed to enter the engine.
Essentially you can manually adjust the fuel flow from a #1 main jet to a #125 main jet
(OEM is a #72.5 main jet).

You can replace the static jetting by removing the carburetor from then engine and
remove the bolt that holds the bowl onto the bottom of the carburetor. Using a small
screwdriver, remove the brass jet that's screwed into the housing stem that protrudes
from the bottom of the carburetor. The Adjustable Main Jet Kit includes directions and a
drill bit to modify the size of the OEM main jet. You replace the modified main jet and
then instead of replacing the bolt you screw into the carburetor the adjustable main jet.
Now you can turn the thumb screw on the bottom of the adjustable main jet to control the
fuel flow.

Once the adjustable main jet is installed, to adjust it you place the snowmobile on a stand.
You start the engine and hold the throttle wide open and begin to unscrew the adjustable
main jet until the engine runs rough. Now screw the thumb screw in until the engine is
running at its peak. From there you want to unscrew the thumb screw about 1/16 turn to
slightly run rich. You can do this before each heat race.

The one thing I'd recommend is considering using the Arctic Cat adjustable main jet on the
Polaris. The Polaris adjustable main jet uses a foot long cable and housing and it becomes
rigid and non-flexible. You can make a slight change and the vibration of the snowmobile
will slowly adjust the main jet back to where you don't want it. The Arctic Cat adjustable
main jet has no cable and therefore has no position memory. Reaching the adjustable main
jet is more difficult, but in my opinion well worth the trouble to ensure a properly tuned
engine.

Clutching

There are several clutch options you'll hear about out there. What I've found is that not
too many people have spent enough time testing clutches to really know what they're
talking about, and that goes for vendors also. They'll sell you clutch after clutch every
time you burn one up and it's always your fault. That's not true of course. It's that they
are being shipped improperly configured for snowmobile racing. Nearly all clutches are
manufactured for go cart racing and we vendors purchase them for snowmobile racing.
There's a huge difference between cart racing and snowmobile racing, and the setups are
completely different. Some venders by what the manufactures are selling and just ship
them out to a snowmobile customer.

I order many clutches and I have to configure every one for snowmobile racing before it
leaves here. Yes, every clutch is touched by us before you receive it. That's why we offer
so many custom configurations is because we are in the clutch anyway, why not sell you
what you need instead of lots of extra parts you don't need. I have personally done over
seven years of testing including having a dyno that tests clutch engagements and lock-ins,
which nobody else has that I'm aware of.

Ice racers in stock classes are required to run with a stock configured clutch. The
difference in our clutches is that we put the springs in before we ship to you. Most others
are selling you a clutch that's been on a shelf for a long time and the spring is already
stretched out. Our clutches will typically engage slightly higher than our competitions just
because the spring is fresh. This is complete ISR legal since all parts are OEM.

Most sno-cross clubs are now allowing us to modify the stock clutch so that it can climb
the moguls on the course and do not become a hazard. It must be OEM parts, but can be
modified. I was the first to configure the clutches for sno-cross racing and believe that
I'm still the only vendor that offers a custom configuration. This configuration change
increases the engagement from 1800-2000rpm to 2400rpm or 2800rpm, your choice. A
2800rpm engagement gets the sled out of the hole much quicker, but is not so much torque
that it breaks the track loose from the snow and spins. The vast majority of sno-cross
racers are using this configuration.

If you are running with an engine that's producing more than 6 HP, then you can start
looking into more aggressive clutches, such as the Premier Stinger Clutch or the
MaxTorque DragginSkin clutch.

Suspension

Setting the suspension is important in all racing. Stock sno-cross racers need to leave
most of the front suspension as OEM, but will need to take about two inches of travel out
of the rear. OEM setup makes the rear suspension act like a pogo-stick and bounces the
kids off the seat. If you take two inches out of the suspension travel by shortening the
limiter strap or replacing it, this will remove the pogo affect. Some clubs did approve
being able to replace the rear shock(s) to control the rebound of the shocks.

Track Clips

OEM tracks have track clips, but they don't have clips that protect the slide from the
rubber cogs on the track. The OEM clips are only for downward pressure. When the kids
turn the snowmobile the slides are pushed against the rubber cogs and it slows the
snowmobile down significantly. Replacing every other track clip on your track will vastly
improves performance and removes rolling resistance. Polaris requires 28 clips while
Arctic Cats require 32 clips. Clips are around $2.50 each at this time.

Bogie/Idler Bearings

Yes, this is probably one of the single most important things to do. The grease that's in
the bearings of each bogie or idler wheel is stiff, sticky and really slows down the sled. Remove
all bogies, idlers and drive bearings from the undercarriage. Remove just one dust cover
off the bearing to expose the ball bearings. Use carb cleaner, brake cleaner, or some
other powerful cleaner to remove all the grease. Drill a small hole in the side of the dust
cover (big enough for a spray nozzle to fit) and replace the dusk cover back onto the
bearing. This will keep debris out. Now you can use a lithium or silicon based spray
lubricant and spray into the drilled hole. The bearing should be super easy to spin. Now
reinstall all the bogies and idlers to the undercarriage. This will remove lots of rolling
resistance.

Track Tension and Drivers

You want to run your track as loose as possible without the drivers skipping on the track.
The tighter the track, the more rolling resistance. Some clubs will allow for replacing the
front drivers with aftermarket sprockets. These aftermarket sprockets drives off the
window instead of the track cogs and allows you to run a little looser and the sprocket is
slightly larger than OEM. You'll need to ask your club if this is allowed.
Over Boring the Cylinder

Beginning in 2013, any and all stock snowmobiles can over-bore the cylinder by .010". In
stock class this will make a difference if you're running in the front and just falling short.
Justifying the cost of making this modification is up to the racer (or dad).

The Unspoken Sno-cross Mods

Nobody admits to it, but there are many modifications being made that do not meet ISR
rules. The most prevalent are bored carburetors, milled heads, lightened pistons, coated
pistons, shaved keys to advance the timing, twisting cranks or cams, even several titanium
head parts such as pushrods, rocker arms, valve spring retainers, etc. We do offer these
services, but no longer do we ask where customers race or what divisions. We used to turn
away customers that wanted these mods done, but then they'd go to our competitors.
Therefore, ignorance is bliss.

More setup information, step-by-step instructions, illustrations, videos, and links to
products coming soon.