Making a scooter go faster

Peugeot Blaster RS12 (2-stroke) - fastest accelerating 50cc scooter?

As soon as they get a scooter, many people's first reaction is to try to make it go faster. This may or may not be a good idea, especially for 50cc scooters. In many states you don't need a motorcycle license for a 50cc scooter or you may be allowed to ride one at a younger age than required for a motorcycle. While you may call it a scooter, the DMV may not. They may call it a moped (even though you can't peddle it). For example here's the DMV definition in Maine


•A moped is a vehicle with not less than 2 brake horsepower and does not exceed 50 cc's and cannot exceed 30 miles per hour on a flat surface. A moped is equipped with a power drive system that functions automatically and does not require shifting. A moped may or may not have foot pedals - [i.e. a 50cc scooter is classified as a moped]
•An operator's license (drivers license) or a motorcycle, motor-driven cycle or moped endorsement or restriction is required.
•Registration is required.
•A moped must be operated single file and as far to the right at all times, except when turning left.
•Operator of a moped must obey all other traffic laws.

The important facts here is that you don't need a motorcycle license (a regular driver's license is OK), but for this to be legal the scooter (moped) cannot exceed 30mph on a flat (level) road. If it can go faster then 30mph, then it's not legal to ride without a motorcycle license. So if you make it go faster by derestricting it and/or tuning it and you don't have a motorcycle license, you're breaking the law and it's illegal to ride it.

So let's assume you have a motorcycle license and you want your scooter to go faster. What do you do?

If it's a 50cc scooter then it may well have been restricted to 30mph by the manufacturer in order to meet regulations such as described above. If so then you first need to derestrict it. There are usually two or three things that need to be done. The restrictions are:

  • The CDI (ignition module) limits the engine rpm. Typicaly a 50cc scooter might be restricted to 7000rpm.
  • The Variator has an oversized boss to limit maximum speed by not allowing the full range of gear ratios.
  • The carburetor jet is small to limit fuel flow (and meet emission regulations)

All these together limit the scooter to a maximum speed of under 30mph (as required by regulations for non licensed riders). All can be easily removed (either by a dealer or by the owner) which makes quite a bit of difference and increases the top speed to maybe 40mph as well as improving the acceleration. The coast is small, from $5 to maybe $35 and the work isn't difficult. If you buy a new scooter from a dealer, they may even do it for you.

You can replace the CDI or do some surgery on the stock module, which will allow the engine to run at higher rpm. You can remove the oversized variator boss boss which will allow a higher gear and give you a little more top speed and you can install a slightly larger main jet which will richen the mixture slightly and that can give you better performance (but it will use more fuel). If you buy a new scooter from a dealer, they may even do it for you.

Larger scooters (anything above 50cc) don't come with restrictors because there is no need for them. They all require a motorcycle license to ride, so there's no restriction on performance needed in order to stay legal.

There is one fairly simple, inexpensive, thing you can do to any scooter that may improve performance and that's to install a set of variator rollers of the right weight. The weight of the variator rollers affects how the gear ratio of the CVT transmission changes. Lighter rollers mean the transmission holds onto a lower gear for longer, giving you better acceleration (like using the lower gears in a car). Heavier rollers mean the transmission "upshifts" earlier (like using the higher gears in a car, shifting into top gear at 30mph). Heavier rollers may give you a slightly higher top speed, but it may take longer to get there. Ligher rollers may give you faster acceleration but the engine may be running at maximum rpm a lot of the time and the top speed could be slightly lower. The right roller weight for you and your scooter is something you have to experiment with. It depends on the scooter and the weight of the rider. What's best for a 100lb rider probably won't be best for a 250lb rider. The 100lb rider can probably use heavier rollers and get the same acceleration as the heavier rider using lighter rollers. The ideal condition is that the scooter rpms rise rapidly and hold at the power peak (around 7000rpm) when you start off with a wide open throttle. Then as the transmission changes the gearing your speed increases but the revs stay around 7000 rpm. If you want to cruise at a speed lower than your top speed, the rpms should then drop as you back off on the throttle.

For a 150cc scooter, optimum roller weights would most likely be in the 10-14gm range, for a 50cc scooter optimum roller weights would most likely be in the 4-8gm range.

See a selction of Variator Rollers on eBay

Making a derestricted scooter go faster

If the scooter is derestricted and you've optimized performance by selecting the right roller weights for the variator, then the only way to make it go faster is to make the engine generate more power. The only way you can make the engine generate more power is to efficiently burn more fuel. That means you have to get more fuel/air mixture into the engine and you have to make sure that that the extra exhaust gas volume created can get out of the cylinder after combustion. To do this you need to do the following:

  • Use a larger carburetor and/or larger jets.
  • Use a more free flowing air filter
  • Use a more free flowing exhaust system
  • Install a cylinder head with larger/more valves.

In addition you may need an upgraded ignition system (CDI), perhaps one with different or adjustable timing.

Of course you are limited in how much air/fuel mixture you can get into the cylinder(s) by the size of the cylinders. You can increase this with a Big Bore Cylinder kit. This can increase the capacity of a 50cc scooter to 70cc or 80cc. You don't see many big bore kits for larger scooters because their owners are not trying to make their scooters look like a 50cc scooter for licensing reasons.

Note that all these parts have to work together. You can't just bolt on a larger carburetor and expect much because the stock exhaust system won't allow the extra exhaust volume to flow out of the cylinder freely. You also have to make sure you have the right carburetor jetting to give you the correct air fuel ratio (see Scooter Carburetor Rejetting), and that also depends on how much flow restriction there is in the air filter. The parts have to be matched and the system tuned.

You can find a large selection of performance parts on eBay via the links below

If modifying the engine to this extent sounds like a lot of work, it is. It requires time, mechanical skill and knowledge about engines and tuning.

The easy way to make your scooter go faster

There is an easier way of course. If you want your scooter to go 55mph rather than 35mph, sell your 50cc scooter and buy a 150cc scooter. If you want it to go 70mph, buy a 250cc scooter. In the end it will likely be cheaper (especially going from 50cc to 150cc), the scooter will be faster than a modified scooter of lower capacity, and it will be a lot less effort. No mechanical or engine tuning knowledge is required. It will also probably last longer and be more reliable.

Really, the only reason to significantly (i.e. expensively) modify a scooter (especially a 50cc scooter) to go faster is because you don't have a license for a larger scooter. Of course you won't have a valid license for your modified 50cc scooter either since it will no longer be classified as a "50cc" scooter that can't exceed 30mph on a flat road.

If you're a mechanic at heart and want a challenge, or you're racing a scooter in a particular class that restricts engine size, then that's enough a reason to modify your scooter, but if all you really want is a faster scooter, just buying a faster scooter is a far better option! A typical Chinese 50cc scooter might cost you around $700. A 150cc version might cost $200 more. Making that 50cc scooter as fast as a 150cc scooter (if it's possible without it blowing up) could cost you $500 or more. The math is obvious.

See Scooters on eBay