Fuel Management

“Fuel plus air equals motion.”

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Exhaust and intake upgrades are the most popular aftermarket replacement products on the market. The aftermarket alternative parts are much less restrictive than stock thus airflow through the engine is increased. The fuel air ratio is crucial to performance, when there is an increase in airflow there needs to also be an increase in fuel or the system will become unbalanced.

Some performance upgrades such as full exhaust systems throw your air-fuel ratio out of whack requiring an adjustment right of the bat. Other performance upgrades like most slip-on exhaust systems and high flow air cleaners don’t necessarily require an adjustment but will always be beneficial to the performance and longevity of the engine. In all honesty it’s recommended that everyone tune their air fuel mixture after an exhaust or intake modification. Even some bone stock motorcycles can benefit from a tune up due to the high standards of emissions and fuel regulation.

Whether you have a carburetor or your bike has electronic fuel injection will determine the process in which your bike will be tuned. Before you go out and purchase just any fuel management upgrade make sure to educate yourself so you can make a well informed decision. The best place to start is with a basic understanding of the motorcycle fuel system.

Carburetor

“The whole carburetor is greater than the sum of its parts jets” Systems theory reinvented , we hope Bowen doesn’t mind.

S&S Cycle Super "G" Carburetor 401-119

S&S Cycle Super “G” Carburetor 401-119

In very basic terms this is how your carburetor works: Air flows into the engine through the venturi as the flow of air increases it creates a vacuum which draws fuel through the jets. The fuel and air mix going through the venturi as the jets vaporize the fuel. Different jets control certain parts of the throttle opening but they all overlap with one another making a change in one part of the process effect the whole. Thus explaining how your carburetor the “whole” is greater than the sum of its parts, basically if one part is out of alignment the entire system won’t function properly because the individual parts rely on the system to function.

The “parts” can be further broken down through the throttle function percentage:

0-25% idle jet system (pilot air, pilot fuel, pilot fuel screw)

0-35% throttle valve

15-80% needle jet and jet needle control

60-100% main jet

The goal? A nice smooth acceleration from idle to full throttle without any bogging or hesitation. Even the slightest of change can damage the system which is why you should always have your carb re jetted to fit the change you have made to exhaust or intake.

EFI: Electronic Fuel Injection

The Cybernetics of Electronic Fuel Injection

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S&S Cycle Throttle Body X Wedge

Tuning with EFI is more complex in a sense, with a carburetor you use tangible items that make changes such as the jets. Contrarily with electronics involved the changes are made through fuel map programs, black boxes that intercept signals, and more.

Broken down in the most basic form possible, electronic fuel injection is a sophisticated system directed by a computer that determines fuel release based on information collected from multiple sensors and the fuel map programmed to the computer. The computer which controls the system is commonly referred to as the ECM (Electronic Control Module) or the ECU (Electronic Control Unit).

The varying sensors which differ based on which system is being used can send data to the ECM from many parts of the motorcycle. These sensors can collect data ranging from crank position, manifold pressure, air temperature, engine temperature, throttle position, and speed. For example the Alpha-N system monitors and compares the throttle angle to the engine rpm to determine which points of the fuel map to be used. Another common EFI system used often today is the speed-density system which measures the intake manifold volume in correlation with the engine rpm to calculate fuel requirement.

Once the computer receives the data determining the engines operating state the computer compares this data to a stored program of different fueling options or maps. Once an option has been chosen the computer directs the injectors to spray fuel for a given length of time. Much like your brain the computer determines a response when given certain input information from the sensors based on stored memory. Unfortunately like us the computer can only know what it is taught so when you change your fuel-air ratio from aftermarket upgrades much like the carburetor problem the whole system becomes unbalanced. The computer essentially needs to be reprogrammed to make accurate measurements and decisions based on the changes.

If all this sounds complex that’s because it is but the wonderful thing about it is that many companies are making user friendly products that allow you to change maps on the fly.

Aftermarket Fuel Management Options

Aftermarket performance companies are more than happy to supply you with upgrades, some that require a skilled mechanic and others that you can do yourself.

Jet Kits

Dynojet Jet Kit

Dynojet Jet Kit

For your carburetor Jet Kits are broken down into different stages depending on modifications, most kits follow this general guideline:

Stage 1: stock bike with aftermarket exhaust

Stage 2: stock bike with aftermarket exhaust and high flow air filter

Stage 3: mildly tuned bike with aftermarket exhaust and high flow air intake

Some kits have detailed instructions so you can find that jetting sweet spot. Additionally most kits come with everything you need to make changes and get your ride running like a champ. Having a well seasoned mechanic adjust and tune your carburetor up will be more expensive than doing the job yourself but can be well worth it.

Fuel Management System

Vance & Hines Fuelpak 3 126-995

Vance & Hines Fuelpak 3 126-995

The all more complex fuel injection systems now even have fuel management systems you can control from your smart phone. That’s right Vance & Hines created a fuel management system that you can plug-n-play with your smart phone! The Fuelpak 3 from Vance & Hines allows to user to see live sensor data via the app and features a large variety of downloads to choose from. Check back soon for a full review on the Fuelpak 3 from Vance & Hines. If smart phones aren’t for you there are still many other options available to get your fuel injected bike tuned up. There is a wide variety Fuel Management Systems to choose from and many skilled mechanics equipped with the best testing tools to get your bike ready to hit the road.

Now you know the basics of motorcycle fuel systems! Have more questions? Give us a call we have expert technicians on hand to guide you in the right direction! Contact us

2017-01-31T16:53:39+00:00 By |Tech Tips|2 Comments

About the Author:

J&P Cycles Social Engagement and Content Specialist. Motocross racer and motorcycle enthusiast.

2 Comments

  1. Raymond February 11, 2016 at 10:33 am

    I have a 2007 flstf I’m currently running Vance & Hines fuel pak with Vance & Hines 2 into 1 big radius exhaust and screaming eagle air filter
    When I’m riding for awhile and I slow down or come to a stop the bike will shut down if I turn off the ignition and turn it on again it’ll start back up
    If I start it and just let it idle in my garage it’ll idle just fine all day is this a fuel pak problem

    • J&P Cycles February 17, 2016 at 2:25 pm

      in most cases on the Softail it is the ignition switch so that would be the first thing to check
      Thank you,
      Don

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