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General Questions
(Select a question from below)

1. What exactly is a Mini Moto?

2. How do Mini Motos handle in comparison to a full size motorcycle?

3. I'm a concerned parent, are Mini Motos safe for my children?

4. Where should Mini Motos be ridden?

5. How fast do Mini Motos go?

6. Do Mito Motos accelerate quickly?

7. I've heard there are a couple of power bands, what does this mean?

8. Why should I buy Italian powered pocketbike over a less expensive bike. What's the difference?

9. How much does protection gear cost?

10. What additional protection does Mid-South MiniMoto recommend?

11. I understand that 2 cycle engines are high maintenance, are these engines dependable?

12. How hard is it acquire additional parts and accesories?

13. How do I mix gas and oil for my pocketbike?

14. What oil is the best to use in my pocketbike?

15. Will my Mini Moto operate on pump gas?

16. I understand some engines are water-cooled, do they require antifreeze or just water?

17. Are Mini Moto replacement parts expensive?

18. Is it really as fun as it looks?

19. Where can I find a Techincal Primer that will help me understand the components of a Mini Moto?


General Questions

1.  What exactly is a Mini Moto?

A Mini Moto is a miniature GP Racing motorcycle. It stands about 15 to 18 inches high depending on the model and brand weighing anywhere from 35 to 55 pounds. Mini Moto Racing is a rapidly growing sport for both children and adults, and by their nature are just pure fun to ride. Although they may appear to look like toys, the European Mini Motos are built to high quality standards of accuracy and proportion of a world class GP bike.

2.  How do Mini Motos handle in comparison to a full size motorcycle?

A Mini Moto handles much like a larger motorcycle, but because the wheelbase and weight are much less, it changes direction quicker. The front wheel of the more powerful pocketbike models can rise up without hesitation with the application of power; also due to the short wheelbase, they can turn very quickly. This in most peoples opinion adds to the fun factor, but demands that the rider has protective clothing, and is familiar with the bike in question.

3.  I'm a concerned parent, are Mini Motos safe for my children?

Any activity can be "dangerous" if the individual doing the activity does not have the proper know how and has not been educated in how to control the thing he/she is operating.  Any child should obviously have full protective gear including but not limited to helmet, gloves, boots, leathers, pads, chest/back protectors. 

Teaching a child to first ride a bicycle and them being capable at that would be an obvious pre-cursor in the process of  riding a Mini Moto.  Most Mini Motos are geared for speeds of up to 40 MPH or more.
Restrictors are available for pocketbikes that can help govern top speeds.

4.  Where should Mini Motos be ridden?

A Mini Moto is not a vehicle that can be licensed for street rding and should never be ridden on the street. It should only be ridden on hard surfaces with no traffic. With permission, a large parking lot or other privately paved area can be an ideal place to ride as well as a closed racing circuit. Always be aware of your local laws pertaining to this type of recreational activity. Laws can and may vary depending on which state or country you live in.

5.  How fast do Mini Motos go?

Most Mini Motos will accelerate quickly to about forty five miles per hour. The speed can be modified more or less depending on optional
performance upgrades and gearing.

6.  Do Mini motos accelerate quickly?

Yes! However this may not be true for all Mini Motos, Some Minimotos are known to have fantastic acceleration speeds. Be warned, there is a huge difference when comparing to lower cost non-European bikes.

7.  I've heard of a power band, what does this mean?

Powerband is simply the band of revs or rpm's where the engine produces the most power.  In some high performance two strokes it feels like something extra "kicking in" but it is just the characteristics of the engine.

8.  How much does protection gear cost?

Prices can vary depending on the level of protection that you desire as a rider. Regardless of this level, we highly recommend that all riders should wear a good helmet, gloves, riding jacket, riding pants or jeans with knee sliders and high top shoes. Most racers wear full racing suits, safety is vital to the health of both the driver and the sport, and should be a primary concern. Feel free to visit our apparel category for additional information and pricing details on riding apparel.

9.  What additional protection gear does Mid-South MiniMoto recommend?

When considering extra protection you must consider all areas that might be injured if you became separated from the bike at speeds. Usually this means helmet, gloves, riding jacket, riding pants or jeans with knee sliders and high top shoes. In addition to these basic items we recommend leather motorcyle riding apparel when racing or riding at high speeds. More than one person has suffered road rash in embarrassing spots when thrown off during a wheelie.

10.  I understand that 2 cycle engines are high maintenance, are these engines dependable?

When broken in correctly,  jetted correctly, warmed up properly before use, and supplied with the correct fuel/oil mixture they are quite reliable.

11.  How hard is it to acquire additional parts and accesories?

All parts and accessories can be obtained through most pocketbike vendors, such as Mid-South MiniMoto, which covers the entire spectrum of parts. We provide pretty much each and every part available for a Mini Moto, and can normally have them shipped the same day.

12.  How do I mix Gas and Oil for my Mini Moto?

A common tool used for this is a "Ratio Rite".  It will help you accurately mix the correct amount of oil in with your fuel.  Be sure to read your owners manual before fueling your Mini Moto.  A new engine should have a richer mixture for the first tank of fuel to help with proper break in. Do not use a mixture of less than 40 to 1 as it will be too rich and may foul the spark plug.

13.  What oil is best to use in my Mini Moto?

We recommend any quality name brand 2 cycle oil (pre-mixed), which can be found any motorcycle / atv store. Our personal brand that we use is Dumonde Tech.  There is a "break in" oil as well as a synthetic oil that can be used after the bike's engine has been properly broken in.

14.  Will my Mini Moto operate on pump gas?

Yes, however we recommend the use of fresh premium pump gas.  A commonly used best practice is to mix only the nessecary fuel/oil for the duration of riding for that day or weekend.

15.  I understand some engines are water-cooled, do they require antifreeze or just water?

We recommend distilled water in water-cooled engine along with a product such as "water wetter". Insuring that they are drained during the winter season to avoid freezing.

17.  Are Mini Moto replacement parts expensive?

No. Most Mini moto parts are reasonably priced and inexpensive to purchase.

18.  Is it really as fun as it looks?

No. It's MUCH more fun than it looks!


Benchtop Basics 101>Mid-South Minimoto's Pocketbike Technical Primer>


 Mid-South Minimoto's Mini Moto Technical Primer







Two Stroke Engines

Two Stroke Engines



Two-stroke Engines are a marvel of engineering simplicity and efficiency.  They extract more hp per lb. than four stroke engines, and have far fewer moving parts.  In fact, most Mini Moto engines have only 3 major internal moving parts - piston, rod and crank.  In a two-stroke engine, the piston acts as the valve(s), opening and closing the intake and exhaust ports located on the cylinder walls.   The two-stroke engine also fires each time the piston reaches the top of its travel (Top Dead Center, or TDC), unlike a four stroke engine which fires only every other time the piston reaches TDC.  This doubling of the actual time the engine spends making power (as opposed to coasting through passive cycles) is largely responsible for the increased efficiency in the two-stroke design.  As in a four-stroke design, a flywheel is employed to store inertia (rotational energy) to help push the reciprocating parts through their passive cycles.

Two stroke engines also are often favored by motorcycle racers because of their characteristically strong powerband.  They are difficult to tame, but few things can compare to the thrill of riding a two-stroke motorcycle.  While a four-stroke engine may pull fairly evenly from a relatively low RPM, two-stroke motors, due to their design, function best and most efficiently at a relatively narrower and higher RPM range than four-strokes.  This is why they are often described as being "peaky".  When they reach this point of maximum efficiency and power (the peak of the powerband) they provide a dramatic rush of power, and a kick-in-the-pants feel that has no equal in the four-stroke world.  Because the focal point of this power peak can be effectively manipulated largely by changing the exhaust design and its volumetric displacement, a two-stroke engine is often described as going "on the pipe"; when it reaches its power peak.

While all internal combustion engines can be described as merely "e;air pumps"e;, this term is particularly accurate when used describe a two-stroke engine.  There are four basic volumetric chambers in a crankcase reed valve induction two-stroke, such as the Polini engine.  There is the intake airbox, the crankcase, the cylinder, and the exhaust's expansion chamber.  These four volumes, when manipulated, can all effect the hp output, and the powerband's location in the RPM range.   Each volume tends to act as an air "e;spring"e; and tuning each volume will affect the motor's performance, as the pulsations of the air within these tuned volumes actually can help to pump and draw air through the motor.  Almost all modifications made to increase the hp of the stock motor will move this powerband upward in the RPM range.

Crankcase reed valve induction 2-strokes, as their name implies, inhale through the crankcase (the carb and manifold are attached to the side of the crankcase) through a reed valve which acts as a one-way "e;doggy door-style"e; valve.

The crankcase is actually a dry sump and it contains no motor oil, so there's no oil to leak out. The crank and other internals are actually lubricated by the 2-cycle oil that you mix in with the gas at a ratio of 50:1 (use a good semi-synthetic 2-stroke racing oil available from any motorcycle dealer). The suspended oil provides lubrication as the air/fuel mixture flows past the internal parts.

When the piston goes up, it creates a vacuum in the crankcase, drawing air-fuel mixture from the carb and past the reed valve which gets pulled open by the vacuum signal, thus admitting air/fuel into the crankcase, filling it. When the piston reaches the very top of the cylinder, the spark plug fires, lighting the fuel mixture in the combustion chamber, which explodes and expands rapidly.  This pushes the piston back down, creating positive pressure in the crankcase, snapping the reed valve shut as it compresses the fresh air/fuel mixture that is now in the crankcase. The air/fuel mixture being compressed in the crankcase is known as pre-charge.

As the piston moves down, it exposes exhaust ports on the side of the cylinder, and the spent exhaust gasses begin to rush out of the ports. The exhaust is also ushered out by a rush of incoming fresh intake gasses, now entering via the intake ports located on the opposite side of the cylinder, which are the next ports to become uncovered as the piston continues downward.

When the intake ports open, they allow the pressurized "e;pre-charge"e; mixture to rapidly squirt from the crankcase into the top of the cylinder, through the transfer ports located along the sides of the cylinder that run down to the crankcase.

The piston then comes back up, closing off the ports; while below, the vacuum draws in more fuel through the crankcase, already beginning the next intake cycle. After the ports have been closed off by the rising piston, the mixture is further compressed by the piston rising until it reaches the top. The spark plug fires when the piston reaches the top, exploding the mixture and sending the piston down, and the whole process begins again.






The reed(s) on a reed valve induction engine function essentially as a one-way doggie-door, admitting air when the motor is drawing air/fuel mixture, and closing when crankcase compression (known as "e;pre-charge"e;) begins.

There are two types of reed petal materials commonly used, fiberglass and carbon fiber. Fiberglass reeds have relatively low spring tension, so they instantly respond to pressure changes in the crankcase (known as "e;signal"e;).  The low spring tension can allow them to flutter at high RPM thereby limiting the amount of power.   Carbon fiber reeds are lightweight but relatively stiff (higher spring tension) and designed to resist fluttering at high RPM.  Fiberglass reeds are good for low- to mid-range power and carbon fiber reeds are better for high RPM performance.

The Polini carbon fiber reed set comes four in the package - a pair of thinner ones (blue), and a thicker pair (green or unmarked).  You can adjust the performance of the motor by using different combinations of these differing thickness reeds, observing that even among the carbon reeds the thinner ones (lower spring tension) will give you better low-end and the thicker ones (higher spring tension) better high RPM performance.


Polini 4.2hp Air-Cooled Engine     Polini 6.2hp Air-Cooled Engine




Polini minimoto engines come in two basic types; Series I and Series II.   They are easily distinguished externally by an easy-to-spot visual characteristic - the area where the carb meets the engine - the intake manifold/reed box.  The Series I (4.2 hp) engine's intake manifold meets the top of the engine case at nearly 90 degrees, and houses a single reed, mounted on a plate.  The Series II engine has a small protrusion from the top of the engine case which allows room for a small reed box containing two reeds, each split to provide a total of four "e;petals"e;.  The Series II engine's intake manifold appears to meet the engine case at approximately 45 degrees.  A four-petal reed kit is available to retrofit the Series I engine.   The other difference between the 4.2 hp and 6.2 bikes (besides the engine case and reed box) is the exhaust pipe.






The Polini racing crankshaft is essentially identical to the standard crank, with the exception of being "e;stuffed"e; with added spacers for volumetric displacement.  These spacers displace additional crankcase volume, upping the "e;pre-charge"e;, and thus the effective final compression ratio.  A case splitter tool is required to split the engine halves for installation.


Cylinder Kit




The standard Polini minimoto engines (both Series I and Series II, liquid-cooled and air-cooled) displace 40cc (39.97cc) and come fitted with a cylinder barrel that has 3 transfer ports to carry the air fuel mixture from the crankcase to the combustion chamber.  Upgrades include a 5 transfer port 40cc barrel (no longer available in air-cooled).  The 40cc five transfer port engine kits even come with the racing crank.  Early Series I engines require a small clearance modification to the engine case to allow the fitting of this kit.

A 5 transfer port race-prepared cylinder is also available (water-cooled only).  This cylinder barrel features additional porting done at the factory for increased airflow.  Note: This cylinder has a raised exhaust port which dramatically raises the RPM of the powerband's onset.  Also available (water-cooled only) is the 50cc "e;Big-Bore"e; kit, which also features 5 transfer ports.  This is one of the most cost-effective upgrades available for the water-cooled engine, as it comes complete with the piston, ring, cylinder, head, gaskets, O-rings, gudgeon pin and circlips, as well as an improved rubber isolated head mounting - a complete top-end rebuild, and a 25% displacement increase in one low-cost kit.

If you wish to know what cylinder is fitted to your Polini motor, use the following Polini cylinder spotter's guide:

315 - 40cc 3-port air-cooled

316 - 40cc 3-port water-cooled

315A - 40cc 5-port air-cooled

316A - 40cc 5-port water-cooled
(you must inspect the exhaust port for evidence of hand porting to determine if it is "e;race-prepared"e;)

316B - 50cc 5-port water-cooled






A Pocketbike uses a stall clutch instead of gears to provide final drive speed regulation.  A stall clutch is actually one of the most efficient means of transmitting power, which is why the fastest internal combustion engine powered vehicles on Earth, AA Fuel Dragsters use them.

The way to set up a minimoto clutch is to have the clutch engage fully somewhere at the bottom of the powerband. If it's in too soon, the bike will bog, and then pick up again as the motor comes back "e;on the pipe"e;.  If it's in too late, the engine will already be making too much power, and the clutch may never fully lock up, causing it to wear prematurely. Obviously, riding it around with the clutch not fully engaged (if you ride like a complete wussy) will burn up a clutch too. You want the clutch fully in just as the motor is going "e;on the pipe"e;, so the transition is nearly seamless.

The older Polini 3-shoe clutch is now out of production. The new Polini 80mm 2-shoe design is fully adjustable for engagement, and also has a spring set available for even further tuning.  Lighter springs allow more rapid engagement, heavier springs provide a more progressive engagement.  If you currently have a 3-shoe clutch, we strongly recommend converting to the new 2-shoe design if you want to extract the maximum power available from your bike, especially if you have modified the engine in any way, because engine mods tend to raise the powerband higher in the RPM range.  When converting to the newer 2-shoe design clutch, the older 78mm clutch drum must also be replaced with an 80mm unit.

The new Polini 2-shoe clutch has an adjustment nut for each shoe's corresponding spring located at end of the spring pushrods. The springs work in compression to resist the centrifugal forces acting on the clutch pawls (shoes).  Tightening the nuts will delay clutch engagement by 150 rpm for each nut flat (adjusted together in pairs). Make sure to always adjust them equally in pairs. Conversely, loosening the nuts will make the clutch engage 150 rpm sooner for each nut flat (adjusted together in pairs) - failure to adjust the nuts equally will cause uneven wear.






The standard tires on the 910 Aluminum framed models (the Carena and Dirt Road) are the 5"e; tires. The optional "e;Big Wheels"e; which come on the 2WB models are commonly referred to as the 6"e; setup (these are actually 6.6"e; front and 6.1"e; rear).  These are tube-type tires, and wear very well offering some of the best available lean angles (some people actually prefer these tires to the newer 6.5"e; T-4 racing tires for this reason).  The 6"e; "e;Big Wheels"e; are just that - bigger WHEELS.  The overall diameter is slightly larger, but only by an inch or so.  The sidewalls are actually shorter than the 5"e; tires, and thus they squirm less, offering faster transient response and better handling, at the expense of some riding comfort.  The 6"e;  "e;Big Wheels"e; for the 910 are the same tires that come standard on the 911 series bikes. Soft compound slicks are available for the 6"e; setup.

The new hot setup for racing is the 6.5"e; tubeless tires, which are available in a variety of compounds, including rain compound. These 6.5"e; tires are standard on the new race-prepared models, the 910 Steel, 911R and new GP/R models in the T-4 compound.   They are also available as an option on the standard 911 series bikes, and are only incrementally larger overall than the 6"e; tires.  They are available in the following 4 compounds:

The T-4 compound tires (Durometer 60) offer awesome grip, great wear characteristics, and even decent wet performance (but not in standing water - they are slick), but they are a little more squat in profile and offer slightly less available lean angles than the 6"e; setup. This is why they are actually less favored by some of the larger riders who cannot "e;hang"e; off the bike as easily as the smaller riders, and need to be able to lean the bike over more.  ...But if you have the courage to hang off and keep the bike more upright and squarely on its tires, the T-4s offer the better grip than the 6"e; and 5"e; setups.

The T-41 compound tires (Durometer 55) are a medium compound and offer a bit more grip, but at the expense of increased wear characteristics.

The R compound tires (Durometer 40) are primarily for rain use, and are available as slicks for hand grooving, or with a hand-cut rain tread pattern.  These tires offer the best possible rain performance, but are extremely soft and will get hot, oily, slippery, and go away very quickly if used in dry conditions.

The B compound slicks (Durometer 65) are a hard compound tire, and are generally not used in competition. These are favored for rental applications for their long wear characteristics.

The recommended tire pressures for the tube-type tires (as converted from BAR) are 17.5 lbs. front, 23.5 lbs. rear.  Adjust these numbers to suit your weight and riding style within the limits of the rated maximum inflation pressure stated on the sidewall (36 PSI MAX for the tubeless racing tires).   You will find that heavier riders will need to adjust primarily the rear tire, because that is where the rider's weight mostly lies on a pocketbike.






One of the easiest ways to manipulate the powerband on a 2-stroke is to tune its exhaust.  While changing the exhaust can radically effect the response of the engine, maximum gains are achieved by tuning other parts of the engine to match.  If you are going to increase the ease of which an engine can exhale, it will obviously run more efficiently, but if you increase the amount in can inhale as well, then the overall results are even stronger.

We recommend re-jetting and/or other induction improvements to compliment exhaust upgrades and to prevent causing a lean condition which could damage your motor. Note: when fitting a racing exhaust to an air-cooled model, some grinding of the cooling fins is required.

With the 910 Carena and Dirt Road models, three pipes are available.  The 4.2 hp pipe, the 6.2 hp pipe, and the racing pipe.

The 911 exhaust pipes come in two flavors; 6.2 and racing.  The racing exhaust features a carbon fiber silencer can and a mellow tone.

The 910 Steel pipe also comes in only two flavors; 4.2 and 6.2.  There is no race pipe available, as the 6.2's lazy-angled "e;Z-style"e; exhaust is very efficient, straightening the flow path and offering significant improvements over other designs.   The 911R also features a more efficient Z-style exhaust.






99.9% of all starting problems are caused by bad / old / improperly mixed gas.  Never use oxygenated fuels or fuels that contain alcohol, as these can cause your bike to run lean, and destroy your motor.  Racing fuels containing alcohol may also cause your bike to run lean, and are best avoided.  Never use gas that has been in storage for even a short amount of time, and definitely don't use something from the can in the garage you bought for the lawn mower sometime last year.

Fuel should be mixed at 36:1 - fresh premium pump gas / high quality 2-stroke lubricant.

The use of racing gas or octane booster is not required.  Octane is a measurement of a fuel's ignition suppression characteristics.  Higher octane fuels will suppress "detonation", or "pre-ignition", (a.k.a. "ping", or "knock") by essentially being "harder to light", and actually burning more slowly.  This way, the high cylinder pressures of some racing engines will not spontaneously ignite the fuel at a point source other than the spark plug, which would result in colliding flame fronts, and detonation.  Unless your motor has increased compression due to a modified cylinder head, or more ignition lead timing due to modifications to the ignition, the use of higher octane fuel will actually produce LESS power.


Spark Plug

Spark Plug



Keeping a fresh spark plug in a 2-stroke motor is exceptionally important, and you should check your plug often.  It is very important to look carefully at the color of the plug as properly "e;reading"e; it can tell you a lot about the engine's state of tune.  The plug's ceramic insulator should ideally be a nice even tan color - this indicates complete combustion, and a proper fuel mixture.









A gray or white-ish plug indicates that the motor is running lean - this can result in engine damage! Clean and check your fuel system for obstruction, check your fuel mixture, check for loose intake manifold bolts and carburetor mounting leaks, failed case gaskets, loose case bolts and leaking crank seals. Anywhere your engine potentially could leak and suck fresh air can be the source of a lean condition.  Switch to a larger carburetor jet if necessary to correct the problem.   Failure to do so can result in engine seizure.

A blackened or oily plug indicates improper combustion resulting from a too-rich mixture, too much oil, or plug misfire.  First check your coil for a healthy spark. Use a fresh plug and ground the electrode to the engine while pulling the starter - the spark should be a healthy blue.  If so, install the fresh plug, and operate the bike normally for a few minutes, remove the new plug and "e;read"e; it.  If it still appears blackened or oily, the problem lies elsewhere.  A hotter plug in not recommended - make sure your fuel mix is correct, and consider a smaller jet only if the bike stumbles or sounds "e;full of snot"e; and doesn't run crisp.

Operating your bike a little too rich won't hurt it - but too lean is never good.  A little dirt in your carb could cause it to run lean, and you wouldn't even know why your bike was running so nice and crisp until it seized.  Because of the many factors that can affect the mixture, including the brand of gas you use, your oil ratio, and even air density, it is imperative that you check your plug often - it can save your motor.  Monitor your plug's color most attentively after any engine modifications to make sure re-jetting is not required to prevent a lean condition.

The 50cc kit, and the air-cooled models require the use of a longer thread plug.  Failure to use the longer thread plug will result in a very large reduction in performance, as the electrode will not extend into the combustion chamber sufficiently.  Use of the longer thread plug in a short thread cylinder head may result in the plug colliding with the piston - this will damage the motor.

We recommend the following NGK spark plugs:


NGK B7HS (short thread) - NGK B9ES (long thread)

Competition use

NGK B7HS-10 (short thread) - NGK BR9EIX (long thread)

The correct plug gap should be 0.6 - 0.8 mm















































This information is the intellectual property of Mid-South Minimoto and may not be reproduced, in whole or in part, unless authorized with the express written permission of Mid-South Minimoto.
Edited by Steve Armentrout
Copyright 2004-2009 - all rights reserved.

This information is provided in good faith as a guide. We are not responsible for any typographical or informational errors or omissions.  Due to the many mechanical and technical variables, this information is to be used only as a guide, and is in no way guaranteed to be accurate or applicable to your engine, your bike, or your world in any way.  HP figures quoted are approximate, and vary from engine to engine due to wear, proper gasket installation procedures, and many other factors.

"e;Your mileage may vary."e;





































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