By: Jason Giacchino
Email: offthepegs@atvsource.com

July 2006

Fuel Injection 101

All the mags keep mentioning how awesome the fuel injection is on the new Suzuki LTR450. If it’s so great, why don’t all quads have it?
Trevor Murray

Trevor, that’s an excellent question that deserves a good answer. To even begin to explain the reasoning behind the praise bestowed upon the modern fuel injection system we have to first take a look at the technology it aims to replace: The carburetor.

A carb flows fuel into the engine intake by relying upon the vacuum produced by the piston inside the cylinder. In other words, the faster that piston rockets up and down, the more fuel gets pulled down from the carb’s float bowl. Once the piston is at rest, however, the carburetor can no longer flow fuel and instead becomes a miniaturized gas tank.

What then determines exactly how much gas will become sucked into the engine with a carb? Jetting; which are basically partially opened ports that meter the flow of fuel.

Fuel injection bypasses the entire float bowl and finicky jets concept and even does away with requiring a vacuum to draw fuel.

Rather, fuel is pressurized via an independent pump (which usually runs off the battery) and is then blasted directly into the engine through an injector nozzle.

Since the fuel flow is no longer dependent upon the piston’s activity, the CDI (ignition computer) is now responsible for determining precisely how much fuel should be injected in direct relation to the situation at hand.

It is important to realize that fuel injection doesn’t actually make any more power than a well tuned carburetor setup. The real advantage of fuel injection lies within consistency. Carburetors are mechanical devices and as such, there are situations where their imperfection causes failure. An example would be riding your quad through a sticky mud bog. Upon nearing the shore you would likely wick the throttle open for an instant boost of momentum to free your machine from the slop. Unfortunately, since the piston would be moving slowly as you eased yourself though, so too would there be little vacuum being created. Suddenly opening the throttle results in more area then the low vacuum pressure can swallow and this is felt immediately as the engine bogs down momentarily.

About the biggest disadvantage to the fuel injection method of fuel flow is that it requires the weight of a battery. ATV models already lugging around a power cell for electric starting duties have little to fear, but this will certainly affect kick-start only, weight conscientious, racers. The other, slightly less significant disadvantage is that the only way to tune a fuel injector is through electronics (which will undoubtedly startle many backyard mechanics). Mods to air boxes and aftermarket pipes will require electronic ignition tweaking whereas presently, simply swapping jets is all that’s required.

Even with such disadvantages to consider, the carburetor’s days are numbered. In answer to your question as to why not all quads come with fuel injection systems: It is still early. Suberbikes have made the transition to fuel injection as have nearly all automobiles. The 450R is simply one of the pioneers in bringing the technology into our arena, an achievement that will most certainly be followed by all of the manufacturers in the near future. This is especially true considering how favorably the press has been reporting on the Zook’s carburetor-less performance.