Time to soup up that tired mini bike with a fresh set of tires, an engine swap, and a few other goodies to let you send it with more torque and speed than ever before!
Monster Moto Mini Bike Mods
Lets face it. You get a cute little 79cc mini bike, and its is lack luster. Once the initial fun wears out, a couple years and wrecks later, you grow out of the weak torque and slow top speed. Your mini bike gets set aside, forgotten, and eventually ends up being sold on the local classifieds. That is where we picked this bike up and juiced it to the max. We stepped in to not only restore, but modify (a.k.a. restomod) this bike to a higher level of power and fun! Lets check it out.
Predator 212cc Engine Swap
First thing is first. The power plant. The stock Motovox, or Monster Moto mini bikes have these 79cc, 80cc, or even 105cc 4-stroke industrial engines. They are great for children who are barely old enough to know how to ride a bike, but when the kids get a bit older, or a big kid trapped in an adult body wants to ride it, it struggles, and bogs down, then eventually tops out at a mediocre speed. Take that weak engine, and replace it with a predator 212cc engine and you basically triple your horsepower right out of the box, and give it enough kick to bring the fun back into a mini bike that otherwise seems like a small children’s toy.
Engine Mounting Plate
When replacing a small engine with a bigger one, you are bound to have to modify things a bit. But don’t worry, if you have a welder, or know a guy that can weld, or can take it to a welding shop, this modification literally took 10 minutes.
This predator 212cc motor mount is a lay in and weld modification. You simply bolt the engine to the motor mount with 5/16″ bolts, line up the rear axle sprocket with a straight edge to the clutch sprocket, and weld the plate in place.
Stage 1 Bolt-On Kit
Bolting on a stock engine always comes with the question:
How do I make my mini bike faster?
It’s an easy answer, but a lot of people make it complicated. You want to keep your torque and acceleration, but make your maximum speed higher. It wont matter if you have a 2 hp 79cc engine, or a 6.5 hp to 7 hp 212cc engine, they all spin at 3600-3800 rpm, making them EQUAL in speed.
What ‘feels’ good is how fast you get there – acceleration.
So how do you get better acceleration, and a higher speed? Unlock the engine’s energy potential by making it operate more efficiently, and install a slightly smaller rear sprocket for a higher top speed (that comes later down in the article) let’s focus on the engine first.
The first step (the one that gives the most torque and RPM gains) is to simply let more air come into the engine through the carburetor, and let more air out of the exhaust. A predator stage one kit is bolt on horsepower. You can expect a few extra horsepower, more torque, and you can even choose to keep the governor in – for now. A typical predator 212cc stage 1 kit includes a high flow intake, intake adapter, a bigger jet for a balanced air/fuel mixture, and your choice of exhaust header. If you are curious about exactly how to install one, you can check out the stage-1 install on this video I made.
Aggressive Tread Tires
With all that extra power under your seat, the stock tires do a pretty good job on and off road. If your tires are worn, or if you want maximum traction, you are going to want to have an aggressive tire that bites into the ground, allowing minimal slip to propel you forward.
I’ve looked at a few tires, and found that the best handling tires with excellent bite, are the 13 x500 – 6 cleat tires, that you can get as a set, one for the rear, and one for the front. What is nice about these ones, is that they are rounded, allowing you to turn and handle the bike well, and the deep cleats keep you planted where you are so you don’t spin out when cornering. The tread is excellent for digging into loose dirt and gravel, with minimal slip.
Heavy Duty Sprocket, Chain, and Clutch
These small mini bikes have small clutches, and small chains. It is almost as if someone poured weaksauce into these things to pinch every penny, the result is flimsy sprockets, and #35 chain that is constantly stretching, breaking, and derailing, even with the supplied chain tensioner. Since you upgraded your mini bike engine from a 5/8″ shaft engine to a 3/4″ shaft engine, you will need to replace your clutch. I chose to go with a 10t centrifugal clutch, 420 pitch chain, and a 50t rear axle sprocket all of which I got as a supplied kit here. This let me gear from a 6:1 gear ratio down to a 5:1 gear ratio (more top speed). Since the engine is already putting out more torque than you need, it can handle the lower gear ratio. It is a win-win all around with excellent bottom end torque, and a faster top speed!
Brakes – Hydraulic or Stock?
With all that extra speed, we found that the stock mechanical brake disc and caliper just needed new pads and an adjustment to be able to stop well enough. However, for maximum stopping ability, there is no substitute for a hydraulic system. Some modification to the mounting area may be required in order for the mini bike hydraulic brake kit to work perfectly. The mini bike hydraulic brake kit we are looking at pre-charged with brake oil, and already has the brake line and calipers pre-assembled. It fits the standard 7/8″ handlebars found on virtually all mini bikes.
The stock twist grip, and cable on these mini bikes is great if maintained properly. Unfortunately, this mini bike was left out in the elements, causing a lot of rust, and ultraviolet damage to the grips. The throttle cable end was frayed, and the grips were a sticky, seized mess. Virtually all mini bikes use a 7/8″ handlebar, allowing us to put on a universal 7/8″ mini bike throttle twist grip. Easy peasy.
The mini bike was almost finished. The performance side was on point: engine, brakes, clutch, tires -check. However, the mini bike still looked like a polished turd with UV faded stickers, and faded plastics (one of which was halfway painted). The vinyl seat was plain black, cracking, and crusty. One of my YouTube subscribers mentioned camo wrapping the bike. I got some red and gray camo wrap, and put it on the plastics. To match the camo, i busted out the old sewing machine and sewed up some black and gray marine vinyl to red welting and stapled it onto the existing seat. It came out great!
The seat of your pants feel with more than double the horsepower, torque, and acceleration is amazing! Handling off road with aggressive tread lets you punch the throttle, and really dig in on the straights and turns instead of peeling out. A final touch of upholstery and vinyl wrap really makes this build a success. Happy riding!
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