#1 Reader Question

TAKING AIM by Chris Maida, Editor

TAKING AIM by Chris Maida, Editor

TAKING AIM, by Chris Maida, Editor

The one question i get most often from our readers is, “Do I have to use a fuel tuner if I install a new air cleaner or exhaust system?” If you have a pre- 2007 EFI machine, one that does not have oxygen (O2) sensors in the exhaust system, the answer is always yes: If the air cleaner or pipes increase air flow through the engine enough to increase its power output, you should install and tune a fuel adjuster of some sort.

The answer for 2007 and later EFI machines is more complicated. In most cases, you can get away with not installing a fuel tuner when you bolt on just a new air cleaner or exhaust system (not drag pipes). That’s what we’ve found on all our installs. In the low throttle settings that the O2 sensors control, the sensors can bring the fuel settings back to stock. Outside of those ranges, The Motor Company usually has enough fuel going in already to cover an air cleaner or exhaust upgrade.

If you do a second upgrade, be it the exhaust or air cleaner, sometimes, but not always, you can again get away with not installing a fuel tuner. However, sometimes doing both upgrades will make the engine run too lean outside of the throttle settings that the O2 sensors control, and you’ll need a fuel tuner. In the low throttle settings that the O2 sensors control, the sensors will probably still bring the fuel settings back to stock.

The easiest way to tell if the engine is running too lean is to bring the bike to a dyno guy you trust, one that has a dyno that can sample the exhaust gases. Have him take mixture readings from each pipe and check the mixtures at different throttle settings, not just wide open. If the mixtures are 14.5:1 or richer (the lower the number, the richer the mix) you can leave it alone. However, you can also install the part and then ride the bike. If it doesn’t spit, buck, or surge while you’re trying to hold a steady speed (try this at all throttle settings), or do anything that it didn’t do before you installed the parts (other than run stronger), you’re good to go.

If you plan on changing both the air cleaner and the pipes, do the air cleaner first. Then ride for a few minutes, varying the throttle settings and checking as just mentioned. This gives the ECM time to recalibrate the fuel settings. If all’s well, then do the pipes. Then ride the bike as you did before. Again, if you have any doubts, don’t risk hurting the engine. Go to a dyno guy you trust and have him check the mixture readings.

Two last points: you can only get by using the stock ECM if you do an air cleaner and/or pipe upgrade. Any other mods, you have to use a fuel tuner. And, only EPA-approved modifications (if there are any), or CARB-approved if you live in California, are legal to do on a street bike.

See you on the road,

Chris

Follow me on Facebook

 

This article originally appeared in issue #307 of American Iron Magazine, published in March 2014.

To order back issues, visit Greaserag.com.

To subscribe to the PRINT edition, click here.

To receive DIGITAL DELIVERY, click here.