Know Your Mini Moto
By Matt Tong
The Mini Moto is a small scale replica of the World Super Bikes used by the likes of Valentino Rossi and ex champion Carl Fogarty. The Mini Moto comes equipped with either a two stroke air or water cooled engine which are, depending on the model, capable of speeds of up to 60Mph.
In this article I will underline the finer points of the components that make these speeds possible.
The Two 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.
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 from 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.
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.
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.
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.
Your new 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.
The tyres on your mini moto are filled with air (pneumatic). Please consult your mini moto handbook for the appropriate psi. It is important to check the tyre pressure regularly, an under inflated tyre will affect the performance of your mini moto, acceleration can become sluggish and cornering can become dangerous.
Before riding your mini moto you need to make sure that the front and back sprockets are aligned and that the chain is perfectly straight running between them. Once you have established this make sure that the chain is tensioned correctly (please see your mini moto handbook). To test the tension of the chain you can manually push the pocket bike, if you hear a ‘pinging’ or ‘popping’ sound the chain is too loose. If the chain is noisy and starts to bind the chain is too tight.
Make sure that the chain is well oiled. The chain needs to be oiled before every ride.
The gearing of you mini moto is dictated by the number of the teeth on the front sprocket and on the back sprocket. The sprockets can be changed as an easy way to manipulate top end speed and acceleration, quite like changing gear on a mountain bike. A front sprocket with more teeth will improve acceleration, however the top end speed will be reduced. A larger rear sprocket will produce a higher top speed but acceleration will suffer. The gearing on your bike can be adjusted in accordance for the track you are intending to ride I.e. a small track with a lot of bends will suit gearing for improved acceleration, however a track with long straights will require a mini moto that is geared for a higher top speed.
The throttle on your new mini moto is a ’twist grip’ style throttle. When you twist the throttle the throttle cable is pulled back revving the engine. It is important to keep this cable free from obstacles and clean. If the throttle begins to feel ‘loose’ of ‘gives’, the tension of the cable can be adjusted via the adjusting screw.
The brake system comprises of brake levers, brake cables, brake callipers and brake discs.
The brakes on your mini moto are operated by levers found on the handle bars. The right hand brake controls the front brake, and the left controls the back brake. Pulling on the handle pulls the brake cable which in turn pulls the lever located on the bake calliper. This action pushes the brake discs towards each other. This creates friction on the brake disc which slows down or stops the bike.
The brakes can be adjusted in the following ways.
The brake cable can be tensioned using the adjustment screw found on the brake lever. Unscrew the locking nut, twist the screw to reach the desired tension. Re screw the locking nut.
This is a two person job. Adjust the screw on the hand brake so that is at the end of its travel. Undo the clamp that holds the brake cable on the lever located on the brake calliper. One person needs to push the lever forward as far as it will, the second person needs to pull back on the brake cable and re fasten the clamp. The crake cable will now be highly tensioned.
To start the mini moto pull slowly to turn the fly wheel. This pumps some fuel around the engine, which lubricates the moving parts. Pull the pull start firmly in order to start the engine. Important, do not pull the cord to the end of its run as it can break. If the mini moto does not start check the choke and the throttle cable.
The choke controls the amount of air that is allowed into the air/fuel mix. The choke is adjusted via a lever located on the side and back of the engine. The choke is off when the lever is down, and on when the lever is up.
When you start the mini moto the choke should be on, when the mini moto is warm and ready to ride the choke needs to be off.
It is recommend that any adjustments to the carburettor are made by a professional. The carburettor pumps and mixes the fuel and air. The small diaphragms, orifices and ports mix the air and fuel very precisely, this process demands clean fresh fuel.
The jet can be adjusted by the screw located in the access hole to the right of the choke lever. The jet is adjusted by the manufacture however the conditions of where you wish to ride may be different, which means that you will need to make adjustments. Turning the screw clockwise will make the bike run with a leaner mixture, and counter clockwise will richen the mixture. Only adjust the screw 1 tern a at time and then test the mini moto, this is trail and error. Please note that it is best to find the optimum setting for performance and then run a slightly richer mixture as a mix that is too lean can seize the engine.
Matt Tong has been importing and riding Mini Motos for over two years. For more information please visit http://www.minimotosandmore.co.uk
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