Ever since I bought my first motorcycle, a 2009 Harley-Davidson XL1200N, I have spent way too much time searching, and searching, and searching through the thousands of forum articles regarding Harley-Davidson EFI management. I have tons of issues with the “lean condition” of new Harley-Davidson motorcycles, including sputtering, pinging, popping on deceleration, and more. I decided at work, when I didn’t want to do work, that nobody else should have to search aimlessly for the [mostly] right answers to these ultra-common and oft-repeated questions. I decided, nobody should have to stress-out about their motorcycle’s EFI system for more than three mouse clicks. So, here you go.
Important: if I missed a question, be sure to respond with (1) the missing question and (2) your best answer. If you disagree with my answer to one of the below questions, respond with (1) the full question and (2) the reason you disagree and your answer.
Note: the answers to these questions include my opinions, not necessarily a “fact”.
Q1: What is EFI? What is EFI vs. a Carburetor?
EFI = Electronic Fuel Injection. All you really need to know about it is that a computer actively controls the amount of fuel that enters your engine based upon a pre-programmed set of ‘if, then’ commands, generally called a “Fuel Table” or “EFI Table”. For example, “if the engine is cold, then run the bike with a rich fuel mixture for five minutes.” EFI is a good thing.
There are three main differences between an EFI and a Carburetor: (1) again, EFI is an active fuel management system that is computer controlled, and often, but not necessarily, uses oxygen sensors to facilitate the management of your fuel mixture. A carb. is not computer controlled, at least not on a motorcycle, and is a far older technology. Since this isn’t an article about carburetors, just understand that they passively inject fuel into your engine. This is why you need to “pull the choke” when first starting your bike, for example. (2) You “adjust” your EFI by reprogramming computer software. This is often made ridiculously expensive, but gives “the brains” (engineers) the advantage over “the brawns” (mechanics), so to speak. You adjust a carb. by physically changing certain parts of the unit itself. (3) EFIs give you infinitely more options to adjust your air/fuel mix, but also allow much less “wiggle room”. There are some other major differences, but we’re keeping it to what you really need to know here.
Q2: Is my EFI-equipped Harley too lean from the factory? If so, why?
The answer is simple: Yes. Why? Because the EPA continues to raise the engine efficiency standards required for new vehicles. In other words, your brand new Harley has to put out a lot less “Greenpeace-pisser-offers” then your ’71 Shovel did. In order for H-D to use the air-cooled, V-twin that makes that signature H-D sound (frankly, relative to H-D’s Revolution engines and others out there, a dated technology), they have to lean-out the fuel mixture in order to meet these standards and sell bikes.
Q3: If I just install new pipes, do I really need an EFI flash or tuner?
Despite what the debate seems to suggest on the forums all over the internet, the answer to this question isn’t hard. Do you NEED to reprogram your EFI? No. Should you, YES! Your bike comes almost dangerously lean from the factory. Freeing up the engines airflow with less restrictive pipes is functionally going to make it run leaner, which, as you’ll read below, is bad. Suck it up, and get yourself a tuner to richen up the mixture and, if possible, manage the timing. Back in the “carbed days”, a minor set if new slip-on pipes didn’t require any work. In these EFI days, 95% of the time, you’re due for at least a $150 ECU reflash – if you can get a dealer to do it.
Q4: What does it mean to “flash” the EFI system?
Flash = reprogram the existing ECU unit with a new set of injection commands. If you’re computer savvy, it’s sort of like flashing the BIOS. If you’re not computer savy, it’s exactly like replacing what was there with something new. Usually these “flashes” are something like $150 and preprogrammed by folks somewhere. You’ll read below what options you have to manage your EFI system, but note that some “race tuners” don’t actually “flash” the ECU, they trick it into doing something advantageous to your air/fuel mixture as directed.
Q5: What’s the difference between an EFI and an ECU?
Nothing, really. I mean, there is but they’re all part of the same system. The EFI is the fuel injection system. So that includes injectors hooked up by wires ultimately to the ECU which is often hooked up to a “race tuner” and/or O2 sensors. If you haven’t figured it out already, the ECU is the computer. God knows what ECU actually stands for, but I’m going to guess: Electronic Computer Unit or Extra Change User.