| Industrial engines. They are still used by | | | | parts on this engine are interchangeable with |
| several manufacturers (most notably Blata on | | | | the Polini. |
| their entry level bike) and typically produce | | | | |
| between 2.5 and 3.5 horse power (hp). All are | | | | What's the difference between the 'series I' |
| air-cooled. Tuning and performance parts are | | | | and 'series II' crankcase?. Fuel is drawn |
| very limited. | | | | from the carb into the crankcase via a |
| | | | one-way valve known as the 'reed valve'. The |
| The Chinese 47/49cc. These engines are used | | | | intake port (where the reed valve and carb |
| in the Chinese made mk2, and mk3 minimotos. | | | | join the engine) on the series I engine will |
| They are air cooled and produce between 2.5 | | | | only accommodate a reed valve assembly with |
| and 3.5 horse power (hp). This engine is | | | | one reed 'petal' whereas the series II will |
| different from the industrial engine that is | | | | take a reed valve 'cage' that accommodates |
| used in the Blata, as it is specifically | | | | two reed petals. A two-petal reed valve will |
| created for mini moto use. | | | | allow more fuel mixture to flow into the |
| | | | engine and, therefore, produces more power. |
| Polini 4.2 engine. This is the basic Polini | | | | |
| engine and, as its name suggests, it produces | | | | Polini Super engine. The super also uses the |
| 4.2 hp in standard form. It is air-cooled and | | | | series two crankcase but with a 5-port |
| uses the 'series I' crankcase with the 3-port | | | | cylinder. It is only available in water |
| cylinder. There is plenty of scope and parts | | | | cooled now but used to come as air cooled as |
| for tuning but few people bother because most | | | | well. To compete with Polini, Mallossi |
| racing classes for the 4.2 won't allow any | | | | manufacture an alternative 5-port cylinder. |
| modifications. | | | | There are no restrictions on tuning supers |
| | | | and with engine 'porting', bigger carbs and |
| Polini 6.2 engine. The top end of this engine | | | | other performance parts they can be turned |
| is the same as the 4.2 (3-port) but is | | | | into awesome machines (for their size) easily |
| available with either water or air-cooling. | | | | producing 12hp. |
| The bottom end uses the 'series II' | | | | |
| crankcase. This helps to make it more | | | | What is meant by 3 and 5 port?. This refers |
| powerful. Race regulations don't allow | | | | to the amount of 'transfer' ports built into |
| modification to the engine internals but do | | | | the cylinder. The transfer ports draw the |
| allow performance parts, the most significant | | | | fuel mixture up from the crankcase and 'dump' |
| being the exhaust. There are a wide range of | | | | it above the piston prior to ignition. A |
| alternative exhausts that year after year | | | | five-port cylinder has potential to produce |
| manage to extract more power from the engine. | | | | more power. |
| Consequently the 6.2 'tag' no longer means | | | | |
| anything, these little rockets (more often | | | | 40cc or 50cc. The 3 port engines are only |
| referred to as 'production' nowadays) claim | | | | available in 40cc. The 5 port cylinder comes |
| power outputs of up to 9hp. | | | | in both 40 and 50cc. ZPF offer a tuned 5-port |
| | | | polini cylinder with their own 'special' |
| The Chinese made water cooled engine. This | | | | cylinder head. The extra cc gives 25% more |
| engine is very similar to the Polini 6.2 | | | | displacement and, therefore, has the |
| however it is a series 1 crankcase engine. | | | | potential for more power. 50's are more |
| The engine is water cooled and is used in the | | | | common in the USA but they're catching on |
| Origami B1 replica. The engine produces | | | | fast in the UK. The UK now allows them to |
| around 7.5/8.5 horse power (hp) Many of the | | | | race in championships. |