Free and easy
The biggest improvement you can make in your kid’s 120 performance is to reduce friction and rolling resistance. With all of four horsepower in the engine, you don’t have a lot to throw away to these gremlins.
Start with a wheel kit for the rails. You can significantly reduce friction between the track and rails with a good set of wheels. Carlson noted that the best setup for wheels is to space them so that one wheel is centered over a track lug and one in the gap between two lugs at any given time. “If you have the wheels spaced so that they hit lugs and valleys at the same time, you create a bumpy ride and it will scrub speed,” he said. “Take a few minutes to get the wheel spacing set up right and you’ll find better traction and top speed.”
The next big horsepower thief, according to Carlson, is the rear suspension and track. “With such a short length, the track is very stiff and has a hard time getting around the suspension,” he explained. “I would recommend to anyone looking for an edge to draw the suspension in as far as possible with the limiter straps. Drill new holes in them if you have to, but get the attack angle as low as you can. It robs power.”
Carlson also recommends running the track as loose as possible without ratcheting. Finally, a spray bottle of cooking oil or other light lubricant will allow you to spray the drivers, track lugs, bogie wheels and hyfax before each race. “It’s an inexpensive solution for friction, simple to do and doesn’t involve any dangerous chemicals around your kids,” he added. “I had one customer that said he sat and just looked at his kid’s rear suspension and identified any place he thought there might be friction. Those were the places he focused on truing and aligning.”
Bypass the governor
Any Minnesotan will tell you that to get ahead, you need to bypass the governor. In our case, we’re talking about the way the factories control how fast the 120s will go. Cat and Ski-Doo use a calibrated spring to keep the throttle opening under control. Polaris uses a rod to do the same.
Bypassing the governor allows your kid to open the carburetor farther, giving it better performance. To do this on a Z 120, remove the airbox. There will be a 10mm bolt and a pair of 10mm hex nuts at the carburetor. Just to the center from the recoil housing, you’ll see an arm with two springs and a rod attached to it. We’re after the large one that looks like a pipe spring on your sled.
Slip the zip tie in the Sportech Bypass kit through the center of the spring and get it started. Pull the throttle lever to the handle bars and tighten the zip tie until the slack is gone. Carlson warns that, “you shouldn’t pull the tie all the way tight. The governor arm needs between 1/8 and 1/4 inch of movement at full throttle. Without that free play, you could really hurt the engine.”
Once you have the governor bypassed, you can start playing with different gearing combos. If you plan to be gearing with some regularity, we’d recommend a quick change hub. With one of these installed, you can swap gears in short order, as you no longer have to pull the whole system apart.
There is some performance to be gained by raising the 120’s engagement. A Mighty Mini High Performance Clutch offers four different weight configurations as well as limited spring tuning. The installation is quick and relatively simple.
1. Start by removing the clutch cover.
2. Find the master link and open it up. On our Z 120, we had to pull the rear gear to remove the chain, as there is no master link.
3. Remove the 1/2” retaining bolt at the center of the stock clutch. Slide the clutch off the crankshaft. Carefully record and retain any clutch spacers. If your sled has them, you’ll need to use them on the new piece.
4. Slide new clutch onto crankshaft, using stock spacers as necessary. Tighten retaining bolt to 12 foot pound
5. Replace chain, making sure master link clip is toward the inside.
6. Replace clutch guard.
The Mighty Mini clutch uses a six-piece adjustable shoe design to add or remove weight. Carlson explained that the four-weight configuration has proven itself to be the best all-around setup. “This arrangement will provide great performance and improved durability over the stock mini sled clutches,” he said. “It raises engagement from 2300 rpm in stock form to 3200 rpm.”
Engagement speed can be tuned by adding or removing weight shoes. However, the weights should be kept in balanced configurations of 2, 3, 4 or 6. Fewer weights will raise engagement. Carlson warned against jacking the rpm too high. “If you try to raise the engagement too high for the gearing or rider weight, you won’t have enough weight in the clutch to compensate and you’ll slip the clutch. If you find that happening, go back and add another weight to the clutch.”
Once you’re close to dialed in with the weights, the Mighty Mini clutch can be further tweaked by shortening the spring length. “By trimming the spring length you can create a slightly stiffer spring rate,” explained Carlson. “The shorter spring will raise engagement, too. I wouldn’t recommend taking more than 1/2 inch off in total. Do it in short increments and be sure to rebend the hook on the end each time.”
To change weights, remove the clutch from the machine.
1. Remove the snap ring on the front of the clutch and pull the bell housing off.
2. Remove the washer and second snap ring. This will allow you to add or remove weights.
3. Backtrack to reassemble the clutch in its entirety and reattach to the sled. Remember, use a torque wrench to tighten the retaining bolt to 12 foot pounds.
Clutch slippage or hangups
If you hear chattering or see jerkiness at engagement, you’re slipping. There are two common causes for this. First, you could have too much spring tension for the weights you’re running. To fix it, add more weight.
The other cause could be dirty clutch weights. To fix this, pull the clutch apart and spray the weight shoes with carb cleaner and dry them off. Carlson advises using a small file and cutting two small grooves parallel to the crankshaft in each weight. This gives clutch dust a place to collect while keeping it clean.
On the other end of the spectrum, you want to make sure the brake band isn’t hanging up on your clutch. To test, run the sled wide open on a jackstand for 30 seconds. Allow it to come to a complete stop without using the brake. Shut the engine off and feel the brake band. If it’s hot, you’re binding somewhere and need to make some adjustments.
Other things to consider
All driver sprockets have alignment problems. The best way to fix that is to pull them and grind them to fit. All drivers can have mold flashing on them from the manufacturing process. For maximum roundness and minimum friction, pull them and put them on a lathe.
Make sure that the gears are aligned. If they are off, even a little bit, you’re losing horsepower in the form of chain binding friction. Use spacer washers on the rear gear to bring them into alignment.
“Above all,” Carlson concluded, “remember to have fun with your kids. If they’re not having fun, just give it a rest for the day.
“Do your testing with them behind the bars. You can really teach them a lot about how to race and compete by using their heads and hard work. Never forget that they are watching you and how you act. Keep everything above board and teach them about good sportsmanship, it’s a lesson they’ll keep forever.”
you need to get it geared. Doesn't matter what you do with the motor, if you don't change the gear. Get with a company called outerlimits performance. They do nothing but 120's. My buddies will do an honest 35mph!!!
A forum community dedicated to snowmobile owners and enthusiasts. Come join the discussion about performance, trails, riding tips, modifications, classifieds, accessories, troubleshooting, maintenance, and more!