Air/Fuel Ratio:

This is the most overlooked and the most important aspect of the carburetor or fuel injection. If it is right the engine runs great and for a long time, get it wrong and it runs bad and sometimes when you run it too lean it will destroy an engine. A good bit of HP can be lost if your air/fuel ratio is not right.

First off what is air/fuel ratio?

The air/fuel ratio is a measure in units of mass of air to fuel so for the perfect air/fuel ratio of 14.7:1 means there is 14.7 units of air to one unit of fuel. The air/fuel ratio is controlled by how much fuel you add via jetting on a carburetor or a "Fuel Controller" on a fuel injected engine.

Rarely does an engine get the perfect fuel/rato of 14.7 and really you don't want it to either. A number higher than 14.7 is termed as a lean condition and below that is a termed a rich condition. I prefer the term "fat". Most of the time you want it a little fatter for more power and the engine runs cooler too.

If you do trail riding or a style of racing that the engine is not running wide open throttle (WOT) all the time you can get away with it running leaner. A lean engine seems to run better but if it is too lean it will run good til it stops because a lean engine runs very hot. If you have a riding style that requires WOT like desert racing or dune riding you would want a fatter condition so the engine would run cooler. Below is an example of what a lean engine can do, and he got away pretty easy.

I had a customer call me and tell me his head pipe was cracked and he wanted to know why. I ask him had he rejetted his carb and he said a mechanic friend had and he changed the main jet from the stock 145 main jet to a 130 main jet. I quickly replied there lies your problem and he replied but it runs so good. I agree very much that a lean engine runs good but not long. His ran so hot that it cracked his head pipe, maybe that is all the damage he got away with.

Now that I still have your attention. How do I get the most power and make sure I don't harm my engine?

Well now that you have spent thousands on your ATV even more on accessories and performance goodies such as a CDI and a fuel controller, why not spend a little more to get a wide band air/fuel gauge? The simple answer is you should and I can't figure out why someone has not done this before. What got me to understand the need to know the air/fuel ratio was the purchase of our Dyno with a air/fuel module. You don't have to go and spend $17,000.00 like I did, just $264.95. I found out how much off you could be by tuning a carb or fuel injection by conventional methods. Take the new carb set up I was working on for the Yamaha Rhino, out of the box the carb was running bad. I set the Rhino on the dyno, installed a O2 sensor in the exhaust and after an hour or so it was all dialed in by adjusting the air screw, jet needle and changing the main jet. Without a air/fuel gauge it would have taken days to get it close and I would not know if I was doing damage due to a lean condition because it was running so good without a air/fuel gauge.

Example:

Say you buy a Dobeck or Dynatek fuel controller for your fuel injected ATV because you did a airbox mod and added an exhaust. Simply install the weld in bung in the exhaust that comes with the air/fuel gauge we sell, screw in the O2 sensor, make the electrical connections for the gauge and go ride. At idle check what number the gauge has, if it's lean turn the low screw on the controller, ride down the road at mid-throttle check the number, turn the mid screw, hit wide open throttle again paying attention to the number and make the necessary adjustments to the high screw on the controller and your done. Now this is a simplified example but it is really not much more difficult than that.

This works for engines with carburetors too, but instead of turning screws, you adjust the air screw, needle positon and main jet size.

Now that the air/fuel ratio is set for your new parts, what do you do with your air/fuel ratio gauge? You can simply remove it, screw in the supplied bung plug and use it again if you do any more engine mods such as pistons, cams etc. Or if it starts running bad for some unknown reason use it for dignostic tool to see where your troubles are.

You say my car or truck does not have to have an air/ratio gauge and it is fuel injected. This is because car and truck injection systems use a O2 sensor in the stock system and adjust the fuel injection itself therefore you don't need the gauge or fuel controller.

I can't for the life of me see why you would not use one, we do on all our Hunterworks (High Tech HP) ATV's and UTV's.

It may seem we are pushing the air/fuel gauge we sell but if you don't buy ours then buy one from somewhere and save yourself a alot of time and money. If you don't buy the one we sell, make sure the one you buy is a wide band.

For addtional info shoot me an e-mail at:

todd@hunterworks.com