The principles of tuning 2 stroke engines are identical whether you are tuning a race bred Suzuki RG500 gamma or a bicycle engine.  The over riding principle of 2 stroke tuning is that all components have to balance.

4 stroke engine, components are typically tuned in isolation from each other.  In other words, improvements in one component results in a benefit to performance.  In a 2 stroke engine, improving one component can have a detrimental effect on the performance of the engine.

We can be frustrated when we purchase a new power part and, after fitting, find that there is no power improvement.  Often, there can be a reduction in power when fitting a performance part.

The tuning principle here is that we have to balance carburation, port timing, ignition timing, exhaust and inlet each time we change a component.

The next principle that differs from 4 stroke engines is fuel : air mixture.  This is very different on 2 stroke engines.  Bicycle engines will run faster with lean fuel : air ratio.  By running a very lean mixture you will, typically, improve the performance.  There is, however, a trade off. The leaner you run the carburation, the hotter the engine will run.  This is why fast 2 stroke engines have a tendency to blow pistons.  The engines seem to be running great but they soon overheat and melt pistons.

The third principle is to know the limitation of your engine.  An issue with tuning a low cost bicycle engine is that it can become more costly to tune than purchasing a purpose built engine.

The limiting factor of bicycle engines is the engine crank.  In most bicycle engines, the limit is around 4,000 RPM.  You will find that most engines purchased from Amazon or eBay are tuned to max out at these revs.  If you try tuning your engine for higher RPM vibration will be severe and often destroy the motor.

Better motors have “single piece” cranks which will allow the engine to rev to around 6,000 RPM.  This is not to say that tuning is pointless.  Tuning emphasis is usually different on bicycle engines.  We are not looking to obtain the 9,000 RPM of a thoroughbred motocross machine. In bicycle engines we are more often looking to maximize torque in the 4,000 to 6,000 RPM range.  We then gear the bicycle to obtain the speed and acceleration that best suits our needs.

With the above principles out of the way, we can then take a logical approach to tuning.  The important decision to be taken next is the amount of money we want to spend.  Big performance benefits can be obtained reasonably cheaply from a basic engine.  The price for every fraction of BHP grows exponentially once some basics have been completed.

Assuming that you have a reasonable budget.  A fair price for some performance in my view would be around $250.  This then would double the price of a basic bicycle engine.

This budget would allow you to fit all the best performance components for these engines.  If you have limits of spending then I would strongly recommend the following components in order of purchase:

1. Expansion chamber
2. Sports carburetor
3. Speed sprocket
4. Reed valve
5. Performance cylinder head
6. Power ignition
7. Bell air intake
8. NOS (with some reservations)

There are a lot of assumptions with the above list.  For 90% of bikers who want some extra performance the order of the list is good.

Note here that many of the components require additional work to help them perform properly.  Reed valves for instance do little unless the piston or barrels are ported correctly.  Expansions and cylinder heads do little unless carburetion is adjusted.

You will note also that I am reserved about the use of Nitrous Oxide Systems (NOS).  If fitted correctly, they can provide a great burst of power for a few seconds.  They do, however, stress the engine.  A little is great for a much needed boost up that steep hill but I would not recommend frequent use.

note also that the power burst from NOS systems typically only lasts for up to 3 seconds.  If you hold the NOS trigger for longer, the engine starts to miss-fire and choke.