It is common these days to see mini bikes being sold in stores already with performance parts fitted, such as K&N style air filters and performance exhausts, however there is always still more work to be done to these bikes.
They are incredible easy to work on and with such a basic engine the only knowledge needed to work on them is knowing how to use a spanner or a screwdriver.
Here is a list of modifications recommended in order to increase the overall power of the bike, as well as improving the handling and feel of the bike.
It would be an idea to start modifying the mini bike with the larger mods, as with these more performance is gained for the money spent. The biggest modification which can be done to a Mini bike is to get it bored out to a larger engine displacement. Most of these bikes will come with a 47cc (which is actually only 39cc). These engines can be bored out with a racing kit to 49cc. This will improve the power of the engine due to the larger displacement, improving acceleration and top end.
If the mini bike is already 49cc there are kits for sale which take the engine up to 58cc again having the same effects as before.
The next modification it would be wise to make to the mini bike is with a performance exhaust, these come in many makes and models and each style will have a different output to the next, so it is best to look around before jumping in and buying one straight away.
These exhausts work as they have an expansion chamber, which improves performance on any 2-stroke engine. These exhausts are not usually over expensive; the cheaper systems can be bought for under £50, and go up to over £200 for the more expensive systems. These are great bolt on performance parts, and can improve the acceleration of the bike with higher low and mid range revs, whilst increasing top end by up to 10 mph.
These exhausts will really benefit the bike if it has been bored out as well and the difference in performance will be evidently noticeable.
The next modification which could be made to the carburettor, and increasing air flow through the bike. Firstly, add a free flow air filter,(K&N style ones). This will mean the bike can take in more air, and the rule of thumb for any engine is – increased air intake + increased fuel flow = increased BHP.
Therefore this part will help with the performance of the bike, however if an air filter is fitted then the carb will need to be up jetted in order to cope with the extra air, performance is likely to decrease if these changes aren’t made. Buying new jets for the mini bike increases performance as these jets will allow more fuel to be sent through the carburettor. Tuning will need to be done with this to get the air:fuel ratio correct.
It is recommended that if modifying the air and fuel intake of the engine that a carb upgrade is purchased. The standard carburettors in these bikes do not have as many adjustment screws as the performance carbs and therefore cannot be tuned as highly, and the performance benefits will not be as evident.
With these changes the bike should have better throttle response with better acceleration and also higher top end speed. This works very well with the performance exhaust and the extra performance with the bike should be easily recognisable.
Once the Mini bike has been up jetted and a free flow filter and new carb have been fitted then it is time to make some smaller adjustments to fine-tune the bike.
The next adjustment which could be made to the bike would be to add a rocket key, this allows the bikes timing to be improved for pulling away and accelerating, meaning that the throttle response and acceleration will be improved.
It is also likely that the gearing of the bike will need to be changed depending on where it is used. This is mainly done through different sized sprockets, and this will be changed depending on how the rider wants the bike to perform
If a larger sprocket is put on the front or rear of the bike then the top end will be improved whilst making accelerating slightly slower, however if the Mini bike is fitted with smaller sprockets then the acceleration will be improved whilst losing some top end. These sprockets can be changed depending on what track is being raced on.
Due to the modifications made to the bike to improve performance, some other changes will need to be made to the bike so it can cope with the extra power and maintain that good performance. Items such as an NGK spark plug or similar could be used. The standard plugs in Mini bikes are not very reliable and will not be able to cope with the power the bike is producing.
Also doing this will improve the starting of the bike as well as keeping the bike performing at its best all the time. Whilst changing this is it also a good idea to change the lead and coil going to the spark plug for maximum benefits.
Another aspect of the Mini bikes which could be tuned is the clutch system. The clutches on the bikes are automatic centrifugal clutches, which will wear very quickly if modifications are made to the bike. It is advisable to upgrade the clutch to a heavy duty clutch with heavy duty springs, these will last a lot longer and also can improve acceleration and throttle response of the bike.
With all this power now added to the bike it is advisable that you make changes to the brake systems on these bikes. Most of them come with half descent disk brakes anyway but upgrading the brakes may be a good idea, imagine racing around a track doing over 50 mph, and then coming to brake and the brakes just ain’t man enough to handle the speed, this is why this change is recommended.
Once all this is done the bike will have been modified a great deal without going too mechanically into it and the extra performance of the bike will leave other bikes standing.
Just remember to always ride on Private land with the owner’s permission and wear protective clothing.