What are misfires?
A motorcycle or car misfire is when the air-fuel mixture ignites not in the cylinder, but in the exhaust. More precisely, it explodes in the hot manifold. When this happens, there is a proper bang and, depending on the bike and the amount of gasoline, sometimes even a flame from the exhaust. That's something you like to see, especially in racing.
What causes misfiring?
There are various reasons for misfiring. But basically it is an unwanted effect and can indicate damage to the motorcycle. For example, the exhaust line may be leaking, allowing fresh air to get in and mix with unburned gasoline. Alternatively, the spark plugs may no longer be working cleanly and the fuel mixture in the cylinder is not being burned properly. However, it may simply be that the tuning of the injection and ignition did not work correctly, and therefore more unburned gas enters the exhaust system. This is the case we will focus on when creating misfire with your 125cc machine.
How can I create misfire with my motorcycle?
In motorsport shows, misfires are created on purpose. To do this, there is a switch on motorcycles or cars that interrupts the ignition. Then really a lot of fuel gets into the exhaust and BOOM! However, on such show bikes, the exhaust manifold and exhaust are also specially processed for this purpose. Otherwise they would be broken after a few shows. But more about that later.
Now first to the technique, how you can misfire with the 125cc motorcycle.
Misfire with method 1
With the first method, you switch the engine off very briefly while driving and then start it up again directly. This way, there is a chance that not every thrust of fuel-air mixture, i.e. the gas, will burn in the cylinder.
This is how you proceed:
Warm up your bike. Only if the manifold is also properly hot, the gas can ignite here!
Now drive on a straight and empty road at about 4000 rpm (what is the perfect gear and the right speed for your bike, you have to try).
Now you give full throttle and turn the key very briefly off and on again. Always keep the throttle at full throttle.
Now the misfires should come! If this is not the case, play around with the gas.
Misfire with method 2
With the second method, you don't have to turn off your 125. With this variant of misfires you try to reach a certain point at which the engine brake still engages but gasoline is already injected.
It works like this:
As with method one, you have to warm up your bike before the backfires!
Now bring your bike up to about 4500 rpm.
Now take your foot completely off the gas.
Now pull the throttle carefully until you reach a point where the engine brake still engages, but gasoline is already injected into the engine again.
Now your bike should start misfiring.
Misfire Tips & Tricks
Do not be discouraged if it does not work with the misfires immediately! Every bike is a little different and especially with the 2nd method you must first try around:
Which gear is optimal?
How high should I rev?
Especially with newer bikes it is not so easy to create a misfire. The current 125cc bikes are just tuned really clean and the electronics and mechanics are getting better and better. If you have an older bike or already have a lot of miles down, it may well be easier to misfire.
Does misfire damage my motorcycle or exhaust?
Whether the provoking of backfires harms your motorcycle can be answered with a clear "no"! Theoretically, the unplanned explosion of fuel in the manifold and exhaust will harm your bike. Because the parts are simply not designed for it. Manifold, muffler and especially the lambda sensor can be damaged.
On the other hand, such an exhaust system on the motorcycle is already a robust thing. It is already considered in the production that it can also sometimes come to the misfire and not immediately everything flies apart. So if you don't let it misfire all the time and only once in a while, it should be fine. But we assume no liability ;)
Misfires with the Yamaha YZF-R 125 Video
For the YZF-R 125 from Yamaha we have produced a small video, which takes up some of the tips from above. So if you are a YZF-R rider, this might help you too:
