Editor’s note — As with any modification, be sure the rider is skilled and strong enough for the changes before altering the quad’s performance.
Some young riders are fine with putting around the backyard on their mini quad. The smile on their face says so. However, what do you do when their grin turns to chagrin and they want more from their little 50cc machine?
Many youth quads have integrated safety features that are used to control their speeds and keep young riders safe. We’re all for that, but many of these parts are designed so they can be changed by the parents to adapt the quad to their child’s talents. We had a 2006 KYMCO Mongoose 50 and decided it was time to kick it up a notch.
Our KYMCO two-stroke has three stages to boost its speed. The first stage is to turn the throttle stop screw all the way out. The result is a top speed of around 10 mph. Stage two, is to modify the clutch bushing on the Lil’ ’Goose’s primary fixed sheave. The third and final stage on this ring-dinger is to clip the looped green wire on the CDI box. With these three changes, the Mongoose 50 two-stroke should be able to achieve a max speed of around 30 mph!
Step 1
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Remove the entire left side floorboard. You’ll need a socket or wrench and a Phillips screw driver. Four bolts hold the floorboard to the chassis mount.
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Step 2
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Loosen all the bolts and remove the CVT housing. Each bolt has its own washer and rubber plug — keep track of these!
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Step 3
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With clutch cover removed, you should see the exposed primary and secondary sheaves. The front one is the primary fixed sheave and the rear is the secondary unit. This is a good time to inspect the cover for excess belt dust and excessive wear. Set it aside for now. It’s also smart to make sure the starter gear below the primary sheave is fully seated and in place. It can come loose while removing the cover.
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Step 4
Use an impact wrench to remove the nut securing the front pulley or primary sheave. It sounds worse than it is. Hold the sheave with your hand and pull the trigger. It should come free rather easily.
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Step 5
Remove the the primary fixed sheave. It’s smooth, has teeth and looks like a saw blade or tiny sprocket.
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Step 6
Remove the drive belt and clutch boss (bushing) from the front crankshaft while holding the primary fixed sheave (the inner pulley) in place. The bushing looks like a tiny cylinder and slides on and off the crank.
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Step 7
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Since you’re inside the clutch, you should inspect the sliding sheave, its weight rollers, the belt and cam plate. Be careful! Use caution when removing the sheave, because the roller weights will roll (imagine that) and could fall out. Also, the cam plate has three sliders that can fall off and be lost. Inspect the roller weights for any flat spots. If you find flat areas, you’ll need to order new ones. You should speak to a KYMCO dealer or aftermarket shop if you want replacement weights or would like to try a different mass.
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Step 8
With the bushing removed, you’ll be able to see the lip or shoulder more clearly. You now can do three things: order a new bushing from the aftermarket, insert one from a KYMCO Super 9 scooter or machine the lip off the stocker.
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Step 9
Once you’ve decided which way to go, reinsert the new bushing. However, if you machined off the lip yourself, insert the machined side onto the crank first to ensure any imperfections are hidden within the assembly and don’t make contact with the belt. There should be no reason to force the bushing back on the crank and it should “seat” like the stock piece.
Step 10
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Reattach the belt to the crank.
Step 11
Put on, the primary fixed sheave being careful to align it properly. Next, put on the washer and nut. Tighten the nut by hand until you seat both clutch halves. Then tighten the nut with the impact wrench. Return the cover — being careful to align the rubber gasket and tighten it to KYMCO specifications. Then, reattach the floorboard.
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Step 12
We think 20 mph is good for most youth riders. However, if your kid is extra special, go ahead and clip the greenish wire (governor) on the CDI box, located under the seat. It’s a small wire all by itself coming out of the CDI and quickly “looping” back into the box. (This can’t be done on a Mongoose 50 four-stroke). This should give the KYMCO more juice.
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If your child still needs more because he wants to race or you’re making a super fun pit quad, dig into the aftermarket and find more things to make the KYMCO cook.
However, adding more performance (engine mods, etc.) will require you to dig deeper into the clutch, modifying the rear assembly, its spring and changing to a stronger belt. These mods are necessary because they add durability to the entire assembly, can boost rpm before the clutch engages and improve acceleration out of corners.
