Fuel Injection Part I – the Great Mystery

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April 16, 2010 | By: Patrick Garvin

Gone are the days of “jetting” your carb, or throwing on a “G” or an “E” or any other aftermarket carb claiming to be the holy grail of tuning. Today, it’s all about throttle bodies, injectors, ECU’s and fuel pumps. And with these new winds of change come a storm of misinformation and confusion about FI controllers and which ones do what and do I really need one at all? In fact, let’s cover that question first.

Do I need a FI controller?

Without getting into a long, semantic debate on “need,” I’ll say this: Your bike from the factory is set up with an air-fuel ratio (AFR is the mass ratio of air to fuel present during combustion) of 14.7-1. In and of itself, this is debatable. Most will tell you that this is too lean (lean meaning not enough fuel). Some would say that this is perfect for good fuel economy. 

Both arguments could be true, but in this writer’s opinion, that’s a bit lean — especially for making any kind of power. But it’s not a bad AFR for cruising at highway speeds and getting good gas mileage. A lean motor is also a hot motor as most of you bagger owners can attest, having the insides of your thighs cooked to a golden brown while sitting in traffic. All is not lost though; you can have the best of both worlds. (Note: We will cover this later in Part 2.)

The second part of the “do I need a FI controller” question begs yet another question: 

Do you plan on doing anything else to your bike?

And 99.9 percent of the time, most of us modify the performance of our machines in some way. That can be an aftermarket air cleaner, an exhaust, or both or something more in depth like a cam , big bore and on an on. So let’s say we’re Joe Average biker and we install a new air intake and some sweet new mufflers. What have we done to the air fuel equation? We’ve effectively leaned it out even more. How you ask?  By taking off the restrictive factory parts and replacing them with some free-flowing aftermarket goodies, we’ve increased the ability of our motor to move more air through it — but we haven’t increased the amount of fuel flowing into the motor.

That means we’ve taken a lean-running motor and, made it worse.  So while the bike may look cooler and sound better, chances are the performance is still suffering — especially the rideability of the bike in the 5- to-6-percent throttle range. Most people wouldn’t even give a second thought to this with a carbureted bike. They would have jetted the bike when they added other parts without hesitation. With the advent of fuel injection, this has somehow become a question.

I’m not going to tell anyone they “need” anything, but if it was my bike, there’d be an FI controller on it the second it hit the driveway. The bottom line is this: Fuel-injected bikes need tuning just like carbureted bikes. It’s just that fuel-injected bikes give us a better set of tools to tune with.  Just because you have a fuel-injected ride doesn’t mean you have the Ron Popeil of motorcycles — you can’t “set it and forget it.”

Stay tuned for next week when we’ll talk about the different FI controllers on the market and which one is right for your setup.

Comments: 6 Comments | Categorized Under: Tech Tips

Comments (6)

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im thinking about fitting a terry components terminal velocity III anything to say , thanks

im thinking of a terry components terminal velocity III, anything to say
thanks

When high flow air filter and after market mufflers or pipes are installed does the ECM calibration that the dealer performs after installing the products correct the lean condition?

Doug, to my knowledge the dealer “stage one ECU flash” is just a general map that is put into the bike. While it probably does add some fuel it’s a very generic tune. You would be better suited with a FI tuner of some sort. In part 2 we will cover which controller is right for a person’s bike.

Doug, to my knowledge the dealer “stage one ECU flash” is a general map that is put into the bike. While it probably does add some fuel it’s a very generic tune. You would be better suited with a FI tuner of some sort. In part 2 we will cover which controller is right for a person’s bike.

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