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By: Jason Giacchino
Email: offthepegs@atvsource.com

June 2007 - Off The Pegs

The Mailbag

While I typically devote my monthly column space to musing and complaining, I’ve been steadily compiling questions in desperate need of answers. Without further delay let’s tear into the mailbag.

"My friend and I have an ongoing argument that I’m hoping you can help clarify once and for all. In quad suspension what do the high- and low-speed compression adjusters actually do? My friend says they affect the quad’s handling at high and low speeds, but I don’t think that’s right.  Any help in settling this matter is appreciated."
Alan Walker

It appears you are correct in this friendly argument. The high- and low-speed compression settings do not refer to the speed of the quad but rather the speed of the shock shaft in response to the terrain it encounters. The low-speed compression circuit is responsible for suspension action in gradual elevation changes, rolling mounds, and trail clutter while the high-speed circuit kicks in during flat landings, and when nailing square-edged bumps.

Typically you can identify the two different adjustments on the shock by their appearance alone. The low-speed adjuster generally requires the blade of a screwdriver to turn while the high speed circuit is usually tuned with a special wrench. Remember that both of these settings refer only to the shock’s compression circuits and are entirely different from rebound and preload adjustments.

"What’s the point of tunable end caps for an exhaust pipe?"
Tony Andello

Since the four-stroke has again taken over the field, we are witnessing a flurry of new technology to accompany the trend. Tunable silencer caps are simply a very minuscule means of adding horsepower to a quad at the risk of a louder exhaust note. Conversely choosing a smaller end cap restricts the quad’s ability to expel spent vapor and robs it of power. The benefit there is a quieter quad. The bottom line though is that most pipe manufacturers perform months of testing to produce a cap that finds the happy medium between performance and sound. They do this so that you don’t have to.

"I have a 2006 Yamaha YFZ 450 and love its performance. Some of my riding buddies have Suzuki’s and often brag that their fuel injection gives them the edge over my carbureted motor. Is there any truth to this and does a bigger carb equal more horse?"
JB Davis

The first part of your question is very simple: No, fuel injection makes no additional power over a carbureted engine. The key difference is that fuel injection makes the same kind of power regardless of conditions whereas carbs require jetting alterations to compensate for any factors that affect fuel mixture (elevation, engine mods, etc.). Fuel injection relies on a computer and a fuel pump to deliver the correct blend of gasoline and oxygen to the motor while a carburetor is a mechanical device that flows fuel and air on account of the natural vacuum created as the piston travels through its stroke.

A bigger carburetor does not necessarily mean more horsepower. While a bigger carb has the potential to move more fuel, the speed at which the fuel travels into the motor is decreased. This happens on account of the fact that it is the piston speed that determines the rate of vacuum drawing in the fuel. This means that piston has to turn over quickly and steadily to maintain a powerful enough vacuum to draw sufficient fuel and air.

On the other hand, a smaller carb supplies less fuel and air to the combustion chamber, but it does so with a much higher velocity. So the bottom line is that a bigger carburetor works more efficiently as the rpms are flying (taking away from crisp response down low) and a smaller carb makes crisp low rpm response.

Like the answer to the last question, the manufacturers spend lots of time and money in testing to equip their models with a carburetor that they feel delivers the most performance across the power spread.


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