Air Filter

A mini moto is equipped with an air filter. Some bikes such as the B1 Origami rep liquid cooled and the Mini Dirt bike have a 'cone' style K and N style air filter. The 2005 mk2 mini moto and the B1 Origami Replica air cooled bikes have a standard mini moto air filter. Both air filters purify the intake of air that is sucked into the carburettor. This means that the air filter should be cleaned regularly as the mini moto's performance can begin to suffer as the engine can become starved of air if the air filter is choked with debris. To reach the air filter, remove the bikes bottom fairing, remove the protective cover by unscrewing the holding screws. Clean the air filter in petrol but make sure that the filter is dry before reattaching to you mini moto.

Spark Plug

Making sure that your spark plug is fresh is important in a two stroke mini moto engine. You can tell a lot from the colour of the spark plug. The top part of your spark plug is covered in ceramic insulator which, when brand new is white. This part of the spark plug can change colour according to how your engine is running. The plug should appear as a nice tan colour when the engine is running perfectly, this indicates complete combustion. A greyish or white colour indicates that the engine is running too lean which can result in engine damage. In this case you should clean and check your fuel system for any obstruction, check your fuel mixture, check for loose intake manifold bolts and carburettor mounting leeks, faulty gaskets and leaking crank seals. Anywhere that your engine could potentially leek and suck in fresh air can be the source of a lean condition.
A blackened or oily spark plug indicates improper combustion and is the result of running too rich. This can be caused by too much oil in the mixture or the spark plug could be faulty and misfiring. Check the fuel mixture and replace the spark plug.

Centrifugal Clutch

The mini moto uses a centrifugal clutch to power the drive the sprocket, which in turn drives the back wheel of your mini moto.
When you start your mini moto the clutch spins as the engine ticks over . The clutch is engaged when you pull back on the throttle. The increase in speed of revolution of the clutch makes the clutch expand and grip the inside of the clutch bell which turns the sprocket that drives the back wheel of your pocket bike.
The clutch can be set up in different ways depending on the type of performance that you want from your minimoto. Adjustable clutches are not standard on mini moto's but an after market Polani or Blata style adjustable clutch can be used in your new mini moto. These allow the rider to adjust the mini moto's set up in according to their preference. Setting the clutch to engage too late when the engine has built up too much power may cause the clutch to slip and never fully engage. This can result in excessive wearing. However setting the clutch to engage too early, before the power has built up in the engine can cause your pocket bike to 'bog down', resulting in slow acceleration. The perfect set up is to get the clutch to engage just as the engine has built enough power to rocket the mini moto away, but without making the clutch slip, this is achievable through trial and error.

'Running in'

Your mini moto should be 'run in' for the first 3-4 tanks of fuel. During this period we recommend that you use a fuel mixture of 25:1. This means a mixture that is made up of 25 parts petrol to 1 part of two stroke oil. During the 'running in' period be careful to not rev the engine to its maximum as this can damage the engine. The 'running in' period will allow the moving parts to become well oiled and the clutch and brakes to 'bed' themselves in. After you have run the minimoto on this fuel mixture for 3-4 tanks, check the chain and tighten accordingly, check the tyre pressure, tighten the bolts on the brakes, forks and wheels. You may also need to readjust the throttle settings to allow for the higher revs that changing to a leaner fuel mix produces. The bike should now be ready for a fuel mixture of 50:1.

Mini Moto Engine Info

This article explains the different 2-stroke engine types fitted to the various Mini Moto's available on the market.

Industrial engines: They are still used by several manufacturers (most notably Blata on their entry level bike) and typically produce between 2.5 and 3.5 horse power (hp). All are air-cooled. Tuning and performance parts are very limited.

The Chinese 47/49cc: These engines are used in the Chinese made mk2, and mk3 minimotos. They are air cooled and produce between 2.5 and 3.5 horse power (hp). This engine is different from the industrial engine that is used in the Blata, as it is specifically created for mini moto use.

Polini 4.2 engine. This is the basic Polini engine and, as it's name suggests, it produces 4.2 hp in standard form. It is air-cooled and uses the 'series I' crankcase with the 3-port cylinder. There is plenty of scope and parts for tuning.

Polini 6.2 engine. The top end of this engine is the same as the 4.2 (3-port) but is available with either water or air-cooling. The bottom end uses the 'series II' crankcase. This helps to make it more powerful. There are a wide range of alternative exhausts that year after year manage to extract more power from the engine. Consequently the 6.2 'tag' no longer means anything, these little rockets (more often referred to as 'production' nowadays) claim power outputs of up to 9hp.

The Chinese made water cooled engine. This engine is very similar to the Polini 6.2 however it is a series 1 crankcase engine. The engine is water cooled and is used in the Origami B1 replica. The engine produces around 7.5/8.5 horse power (hp) Many of the parts on this engine are interchangeable with the Polini.

What's the difference between the 'series I' and 'series II' crankcase?

Fuel is drawn from the carb into the crankcase via a one-way valve known as the 'reed valve'. The intake port (where the reed valve and carb join the engine) on the series I engine will only accommodate a reed valve assembly with one reed 'petal' whereas the series II will take a reed valve 'cage' that accommodates two reed petals. A two-petal reed valve will allow more fuel mixture to flow into the engine and, therefore, produces more power.

Polini Super engine. The super also uses the series two crankcase but with a 5-port cylinder. It is only available in water cooled now but used to come as air cooled as well. To compete with Polini, Mallossi manufacture an alternative 5-port cylinder. There are no restrictions on tuning supers and with engine 'porting', bigger carbs and other performance parts they can be turned into awesome machines (for their size) easily producing 12hp.

What is meant by 3 and 5 port? This refers to the amount of 'transfer' ports built into the cylinder. The transfer ports draw the fuel mixture up from the crankcase and 'dump' it above the piston prior to ignition. A five-port cylinder has potential to produce more power.

40cc or 50cc: The 3 port engines are only available in 40cc. The 5 port cylinder comes in both 40 and 50cc. ZPF offer a tuned 5-port polini cylinder with their own 'special' cylinder head. The extra cc gives 25% more displacement and, therefore, has the potential for more power. 50's are more common in the USA but they're catching on fast in the UK. The UK now allows them to race in championships.
The Polini engine components are interchangeable, which can make for some interesting combinations.

Fuel: 2 stroke

The two stroke engine needs to be run on a mixture of petrol and two stroke oil. This is so that the engine is kept lubricated whilst in use.
99% of all starting problems are caused by fuel problems. These can stem from bad or old fuel and improperly mixed fuel (please see mixing chart). Do not use fuels that contain alcohol, as the can cause you bike to run 'lean'. Be advised some racing fuels contain alcohol and are best avoided.. We recommend that you use normal petrol for a garage and a quality two stroke oil.
A mixture that is too lean I.e not enough two stroke oil can damage your mini moto's engine as the moving parts are not properly lubricated. This can cause the engine to seize. However a mixture that is too rich can choke the engine and effect the performance and cause starting problems. You can tell if your mini moto is running too richly by the plumes of white smoke coming out of the exhaust and the lack of performance. A rich mixture (25:1) is needed to lubricate the engine during the 'run in' period, you may experience a lack of performance during this period. The pocket bike may run more slowly and acceleration can be sluggish, however when you change to a mixture of 50:1 you will really notice a difference. The leaner mix ignites in the combustion chamber faster and with a more explosive force than the richer mix. This means higher revs which means more power and acceleration.
We recommend that a fuel mixture of 25:1 is used to 'run in' you mini moto, and a mixture of 50:1 is used thereafter.

The 2 stroke engine

The two stroke engine produces more hp per pound than the four stroke engine. The two stroke engine consists of three moving parts, the piston, the rod and the crank. The piston acts as valve that opens and closes the intake and exhaust ports that are located on the walls of the cylinder. Unlike the four stroke engine that fires only every other time of the pistons movement, the two stoke engine fires every time the piston reaches the top of its travel. This means that the time spent generating power is doubled in the two stroke engine than that of the four stroke engine, as there is no engine coasting during passive cycles. This is the main reason that the two stroke engine can rev more highly and produce more power (for its size) that the four stroke.