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The Haynes ATV Basics Techbook is a do-it-yourselfer's guide for maintaining, buying and riding ATVs, for recreation and utility.
Includes tips on finding the right ATV for you and maintaining it for the long haul. Selecting trailers, plows and other accessories.
Plus how to operate your ATV, safely!
Book Excerpt: ATV Basics Techbook: How To Buy, Maintain and Ride ATVs for Recreation and Utility
FUEL AND EXHAUST SYSTEMS
Floating calipers are widely used on ATVs, with the single-piston type the most common (see illustration). They approach the problem of exerting equal pressure on both sides of the disc mechanically, rather than hydraulically.
The caliper body is mounted in a bracket with sliding pins which allow it limited sideways movement. The caliper body may have one or more pistons; where there's more than one, both face in the same direction.
One pad rests against the piston and the other is contained by fingers on the caliper body. When the brake operates, the piston pushes its pad against the disc surface. Continued pressure causes the caliper body to slide along its pins and away from the disc, so the fingers pull the opposite pad against the other side of the disc.
The sliding caliper design eliminates problems sometimes found with opposed-piston units, where corrosion jams one piston. This leads to unequal pressure being exerted on the two pads, resulting in braking inefficiency.
The drawback with the sliding caliper is corrosion or wear in the sliding pins. This too can cause unequal braking effort and can allow chattering between the bracket and caliper. For this reason, the pins are usually encased in rubber boots.
To obtain even pressure across the surface of each brake pad, dual-piston models use different piston sizes, with the trailing piston being larger.
Rear calipers are usually the hydraulic sliding type and incorporate a mechanical linkage for control of the parking brake (see illustration). As the cable or rod pulls the caliper lever, a screw mechanism (cam) extends to provide pressure.
An exception is the rear caliper on Yamaha YFM350 models, which is operated entirely by mechanical linkages (see illustration).
CARBURETOR | GENERAL INFORMATION
The most common ATV carburetor design is the slide type. In this design, the flow of fuel and air into the engine is controlled by a throttle piston (slide) which moves vertically in the carburetor body.
The throttle piston opens and closes the venturi on demand, allowing more or less airflow as needed.
In the bottom of the throttle piston is a tapered jet needle, which rides in the needle jet. As the throttle piston is lifted, allowing more airflow, it also lifts the jet needle.
The jet needle is narrower at the bottom so that the higher it rises, the less it obstructs the needle jet opening. This allows more fuel flow to match the increased airflow.
The throttle piston is controlled directly by a cable attached it its top.
Yamaha uses a variation of the slide carburetor in its YFM350 models (see illustration). This design incorporates a throttle butterfly as well as a slide.
CONSTANT VACUUM CARBURETOR
Some large-displacement models use a constant vacuum carburetor. Like the slide carburetor, its airflow is controlled by a piston that moves vertically in the carburetor body, and its fuel flow is controlled by a tapered needle that varies the opening of the needle jet.
Subject: Haynes ATV Basics Techbook: How To Buy, Maintain and Ride ATVs for Recreation and Utility. ISBN-10: 1563921472 | ISBN-13: 9781563921476 | Haynes 10450