How to Make My 125CC Motorcycle Go Faster

by Sean Russell
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Once you are comfortable with the power of your 125cc motorcycle, you may want to make it faster. Increased airflow, larger exhaust piping, decreasing weight along with other aftermarket motorcycle modifications will have you rocketing down the track faster than before. A faster 125cc motorcycle gives those who race an advantage and leisurely riders more of a thrill. Caution must be taken after upgrading the performance of your 125cc motorcycle. Increased acceleration and top speed also increase the the chances of bodily harm in the event of a crash.

Step 1

Disassemble the air box and remove the filter. The filter is one of the cheapest components of a 125cc motorcycle but one of the most important. Fuel ignites with the help of air, so the more clean air that flows into the engine the more combustion you'll get. Air filters come in different colors, such as yellow, red or white. This helps riders know when they are dirty. If your 125cc motorcycle air filter is dirty, spray it with cleaner or replace with an oiled aftermarket filter. Also, clean any gunk out of the air box with contact cleaner, making sure no grime or dirt falls in.

Step 2

Check the oil to make sure it is clean. Motorcycles with 125cc engines weigh less then larger displacement motors thus riders have an easier time cornering, which can cause increased changes in throttle and braking. Prolonged braking and bursts of acceleration gunks up lubrication of engine components decreasing overall performance. Refer to your owner's manual to see how often the manufacture recommends oil changes. If you are changing the oil, also replace the oil filter.

Step 3

Replace the stock exhaust pipe with an aftermarket exhaust that includes larger piping. Motorcycles with 125cc engines come with small diameter exhaust piping because of the engine displacement, but that does not mean they will not benefit from larger piping. Increased exhaust piping diameter creates more room for engine waste to exit your 125cc motorcycle. Refer to individual aftermarket exhaust dyno-readings, usually available on the distributor's website, to identify potential horsepower improvements.

Step 4

Check front and rear tire tread depth. Motorcycles with 125cc engines are light, so less weight is on the tires during acceleration, which could cause the tires to slip while accelerating if the tires do not have proper tread. A bald tire will not grip terrain as well as a brand new set, thus reducing potential acceleration and top speed.

Step 5

Upgrade your front, rear or both sprockets for increased power-band control. Motorcycles with 125cc engines lack top speed compared to larger displacement engines. Purchasing a front sprocket with less teeth than stock and a rear with more teeth than stock can help. Each gear has a set power band controlling when it will hit the rev limiter. Sprocket changes affect the power band of each gear. Sprocket upgrades will not increase horsepower, but they will change the gear ratio.

Step 6

Port and polish cylinder heads, which allows more air to flow into the combustion chamber of your engine. This modification requires a machinist to disassemble your motor. The 125cc is categorized as a small displacement motorcycle engine but machining intake and exhaust ports for smoother, increased airflow increases displacement efficiency and leads to higher horsepower.

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