Tuning of two-stroke Motorcycles
Created | Updated Jan 28, 2002
How to make a moped faster (this is engineering stuff!)
The MOPED: Noisy, smelly, two-stroke, small motorcycle (stressing small as it usually has not more than 50 ccm), used by male youths from the age of 14 in all european countries to sound-shock older citizens, prove courage, demonstrate evolving manhood, block inner city pedestrian zones, and yes, to get from A to B at day and night in rain and shine (and snow and ice).
It comes either resembling a bicycle, just a bit bigger (mostly France, Holland, Germany) or a cross / trial bike, just much smaller (Itlay, Spain, Greece). Modern sub-species have a cruiser type of look (like a very small Harley Davidson) but that is just ridiculous and of course a japanese invention.
A Moped is by law forced to go painfully slow and producers implement a number of slowing items to comply with the laws, hence this article.
Disclaimer: This article does by no means intend to encourage young readers of h2g2 to break the law. The below mentioned tricks should only be applied to vehicles that run on race tracks closed to the public. Making your moped faster may mean that its brakes and other structural elements are too weak for the speed. You may loose insurance cover if you run your tuned moped on public roads.
Note: Scooters like the italian Vespa are a completely different story. Where the Moped driver is male, comes from a smaller city or village and is generally more a human of the hand (yes, a macho), scooter drivers are unisex, urban and pretend hard to be intellectual. Also they can be quite old and follow weird occupations (businessmen). In other words: They are sissies.
Note also: This article has been written with a german background (more specifically: Ruhr area). You french, english, irish, danish and other international hobby engineers, please to not hesitate to comment and enrich it.
Now: How to make a moped faster (given the character of its drivers the question of why to make a moped faster is irrelevant)
Theoretically there are two ways to improve speed of your motorcycle, those which are spotted by the police and those which are not. Note however that at least the average german village policeman knows exactly where to look for improvements at your little easy rider (I suppose that the bobbies and flics of other european countries have the same ability. So, in practice the following improvements are both illegal and detectable by police. Think twice wether you want to apply them.
1. Reducing the rear-wheel gear
The classic. As the rear wheel of each moped is driven by a chain much like a bicycle, by building in a smaller gear you get the same effect as if you would switch to a a smaller gear with a mountainbike. You get faster but acceleration also gets worse. Good for flat countryside if it is not windy. Forget about it in the mountains. Smaller gears are produced for nearly all kinds of mopeds by dubious italian firms and should be avaliable in a shop near you. Note that you may have to shorten the chain, too.
2. Take a smaller carburator nozzle
This IS hard to detect by police! The carburator mixes fuel and air into an explosive mixture by ways of sucking the fuel through a small nozzle or jet. By taking a nozzle with a smaller diameter the air-fuel mixture gets less "fat" (is that the right term?), meaning that it contains more air. To a certain extend that makes the mixture more explosive and lets your engine rotate faster. Producers mostly build in too big and "fat" nozzles, turning your engine into the equivalent of a full and dozy bear instead an agressive hungry wildcat. As with the smaller gear, your local shop should also have smaller nozzles.
3. Remove obstacles in the cylinder intakes and exhausts
Producers may have built in reducing discs or other obstacles between a) the carburator and the cylinder and b) the cylinder and the muffler. The obstacles reduce the flow of gasses into and out of the engine and hence reduce its power. Take the engine appart (go ahead, its only a two stroke, no cam shafts, no steering belts, no valves to worry about) and check out the neuralgic places.
If there is no obstacle any more you can further improve power by enlarging the intake and exhaust holes with a grinder (drilling machine).
A weird variation of that: You may coat the insides of the holes with chrome to reduce friction for the gasses to a minimum. This is really weird and I don't know wether it works, but it sounds good, doesnt it?
4. Muffler tuning
It gets noisy! Once you removed obstacles for the gas flow in the cylinder you will consequently also do so with the muffler. The original muffler as it comes from the producer has only one purpose. To choke your engine to near death! How to change that? You can
a) get a bending pipe (first piece of pipe from the cylinder to the actual muffler) with a larger diameter (available again from the named dubious italian firms),
b) take out the end piece inside the muffler (looks usually like a flute) and drill holes into it or just shorten it, or
c) radically take all the crap out that there is in the muffler - that also improves the sound of your moped significantly.
5. Piston tuning
The piston is the part that moves up and down in the cylinder. Its mass (weight) determines its speed within the cylinder. By building in a lighter piston (a "race piston"), your engine revolves faster and lets you drive faster. Where to get a race piston? Again from the named italian tuning companies or by just cutting away the lower part of your original piston and drilling holes into it to take away further unneeded material.
Note: Race pistons may damage your engine after a while (or immediately if you didn't do a good cutting and drilling job).
6. The BIGGER ENGINE option
If your engine has originally 50 ccm, you may just get a larger kit (piston and cylinder) with, lets say, 80 or 120 ccm. This is artless, however and I do not approve it. If you want to do it, find out yourself where to get those kits.
So that's it. I would be happy if this article could grow into a full compendium of small-engine art, so please contribute!
The MOPED: Noisy, smelly, two-stroke, small motorcycle (stressing small as it usually has not more than 50 ccm), used by male youths from the age of 14 in all european countries to sound-shock older citizens, prove courage, demonstrate evolving manhood, block inner city pedestrian zones, and yes, to get from A to B at day and night in rain and shine (and snow and ice).
It comes either resembling a bicycle, just a bit bigger (mostly France, Holland, Germany) or a cross / trial bike, just much smaller (Itlay, Spain, Greece). Modern sub-species have a cruiser type of look (like a very small Harley Davidson) but that is just ridiculous and of course a japanese invention.
A Moped is by law forced to go painfully slow and producers implement a number of slowing items to comply with the laws, hence this article.
Disclaimer: This article does by no means intend to encourage young readers of h2g2 to break the law. The below mentioned tricks should only be applied to vehicles that run on race tracks closed to the public. Making your moped faster may mean that its brakes and other structural elements are too weak for the speed. You may loose insurance cover if you run your tuned moped on public roads.
Note: Scooters like the italian Vespa are a completely different story. Where the Moped driver is male, comes from a smaller city or village and is generally more a human of the hand (yes, a macho), scooter drivers are unisex, urban and pretend hard to be intellectual. Also they can be quite old and follow weird occupations (businessmen). In other words: They are sissies.
Note also: This article has been written with a german background (more specifically: Ruhr area). You french, english, irish, danish and other international hobby engineers, please to not hesitate to comment and enrich it.
Now: How to make a moped faster (given the character of its drivers the question of why to make a moped faster is irrelevant)
Theoretically there are two ways to improve speed of your motorcycle, those which are spotted by the police and those which are not. Note however that at least the average german village policeman knows exactly where to look for improvements at your little easy rider (I suppose that the bobbies and flics of other european countries have the same ability. So, in practice the following improvements are both illegal and detectable by police. Think twice wether you want to apply them.
1. Reducing the rear-wheel gear
The classic. As the rear wheel of each moped is driven by a chain much like a bicycle, by building in a smaller gear you get the same effect as if you would switch to a a smaller gear with a mountainbike. You get faster but acceleration also gets worse. Good for flat countryside if it is not windy. Forget about it in the mountains. Smaller gears are produced for nearly all kinds of mopeds by dubious italian firms and should be avaliable in a shop near you. Note that you may have to shorten the chain, too.
2. Take a smaller carburator nozzle
This IS hard to detect by police! The carburator mixes fuel and air into an explosive mixture by ways of sucking the fuel through a small nozzle or jet. By taking a nozzle with a smaller diameter the air-fuel mixture gets less "fat" (is that the right term?), meaning that it contains more air. To a certain extend that makes the mixture more explosive and lets your engine rotate faster. Producers mostly build in too big and "fat" nozzles, turning your engine into the equivalent of a full and dozy bear instead an agressive hungry wildcat. As with the smaller gear, your local shop should also have smaller nozzles.
3. Remove obstacles in the cylinder intakes and exhausts
Producers may have built in reducing discs or other obstacles between a) the carburator and the cylinder and b) the cylinder and the muffler. The obstacles reduce the flow of gasses into and out of the engine and hence reduce its power. Take the engine appart (go ahead, its only a two stroke, no cam shafts, no steering belts, no valves to worry about) and check out the neuralgic places.
If there is no obstacle any more you can further improve power by enlarging the intake and exhaust holes with a grinder (drilling machine).
A weird variation of that: You may coat the insides of the holes with chrome to reduce friction for the gasses to a minimum. This is really weird and I don't know wether it works, but it sounds good, doesnt it?
4. Muffler tuning
It gets noisy! Once you removed obstacles for the gas flow in the cylinder you will consequently also do so with the muffler. The original muffler as it comes from the producer has only one purpose. To choke your engine to near death! How to change that? You can
a) get a bending pipe (first piece of pipe from the cylinder to the actual muffler) with a larger diameter (available again from the named dubious italian firms),
b) take out the end piece inside the muffler (looks usually like a flute) and drill holes into it or just shorten it, or
c) radically take all the crap out that there is in the muffler - that also improves the sound of your moped significantly.
5. Piston tuning
The piston is the part that moves up and down in the cylinder. Its mass (weight) determines its speed within the cylinder. By building in a lighter piston (a "race piston"), your engine revolves faster and lets you drive faster. Where to get a race piston? Again from the named italian tuning companies or by just cutting away the lower part of your original piston and drilling holes into it to take away further unneeded material.
Note: Race pistons may damage your engine after a while (or immediately if you didn't do a good cutting and drilling job).
6. The BIGGER ENGINE option
If your engine has originally 50 ccm, you may just get a larger kit (piston and cylinder) with, lets say, 80 or 120 ccm. This is artless, however and I do not approve it. If you want to do it, find out yourself where to get those kits.
So that's it. I would be happy if this article could grow into a full compendium of small-engine art, so please contribute!
