Motorcycle engines are powerful yet delicate machines; optimizing your air-fuel ratio is the key to obtaining optimum performance and reliability. There are a variety of aftermarket parts and accessories that can be used to unleash the hidden potential of your bike.
It's not necessary to be a professional mechanic, but understanding how the air-fuel ratio affects your engine can make the difference between first place and getting left in the dust. There is an ideal air-fuel ratio for every motor that gives the best performance, when the amount of fuel in the mixture is greater than ideal this is referred to as a "rich" condition, and when the amount of fuel is less than ideal it is called "lean."
Symptoms of a lean condition may be:
- Decreased power
- High idle
- Excessive heat
- Pinging or detonation
In extreme cases a lean condition can lead to overheating and engine damage. Symptoms of a rich condition include:
- Poor throttle response
- Carbon deposits/black smoke
- Spark plug fouling
- Odor of unburned fuel in exhaust
Motorcycle Air Filter
Why do you need a new air filter?
- Existing filter is dirty and its life is spent
- Upgrade for better performance and filtration
- Upgrade to compliment other modifications like exhaust and engine work
Replacing a bike's OEM air filter from the start is not a bad idea unless you prefer to get your money's worth and then upgrade. In any case, an aftermarket air filter like one from BMC and K&N offer numerous benefits over the stock filter.
- Better filtration
- Better air flow
- Cost effective
Upgrading to a high-performance air filter is simply the first step in fuel management. Without other modifications the new air filter can be detrimental to your bike. Therefore, a high flow air filter goes hand-in-hand with a jet kit or fuel controller.
Motorcycle Jet Kits
If your bike is carbureted then a jet kit is what you need to dial-in the air-fuel mixture. (If your motorcycle is fuel injected see Fuel Controller below) Jet kits usually include:
- Several different sizes of replacement main jets
- Drill bits (occasionally)
- Jet needles
- Pilot jets
A jet kit changes the fuel to air ratio which you need when adding a new high-flow air filter. Why you need a jet kit:
- You modified your ride (air filter/exhaust/engine work) and want to get the maximum performance
- You want to increase power or improve the way the bike runs
- Changes in altitude
Jet Kit Installation
Installing jet kits requires you to remove your bike's carburetors. How difficult this process is depends on the type of bike. Different kits are available for different purposes.
- A Stage 2 jet kit is meant for a bike with an aftermarket exhaust and high-flow air filter and stock engine
- A Stage 3 kit is meant for a mildly tuned engine with an aftermarket exhaust and air filter
- Choosing the right jets sometimes requires trial and error - this can be time consuming depending on how much effort it takes to reach the carburetors.
Unless you are proficient around motorcycle engines we suggest finding a reputable bike shop to help you install a jet kit. A bike shop with a dyno can help you choose the best jets minimizing the trial and error period.
Dynojet makes one of the more popular Jet kits on the market.
Motorcycle Fuel Controller
A fuel injected motorcycle uses a fuel controller for tuning. Installation is fairly simple but the main challenge is gaining access to the electrical connectors that the fuel controller plugs into.
Tuning a bike with a fuel controller is generally done with a computer - new settings for your bike are saved as a "map" that the controller uses to adjust the amount of fuel delivered to your engine. Most manufacturers make custom maps available online, however it is best to have a shop with a dyno create a map specific to your ride.
Some fuel controllers offer other benefits, including:
- Multiple maps: allows you to switch between two or more maps. For example, if you want to switch between pump and race fuel
- Quick shift: using an additional switch or sensor. This feature allows you to up-shift at full throttle without using the clutch
- Traction control: certain models have a traction control function which helps reduce wheel spin and improve lap times
- Auto tune: using an oxygen sensor, some fuel controllers can tune a custom map while you ride
Written By: AndrewT