ATV Basics Techbook: How To Buy, Maintain and Ride ATVs for Recreation and Utility

FLOATING CALIPERS

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

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

SLIDE CARBURETOR

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.

Chapter 1 — Types of ATVs
An overview | Drive systems | Engine types | Brake systems

Chapter 2 — ATV Terminology

Chapter 3 — ATV Buyer's Guide
Determining your needs | Inspecting the used ATV

Chapter 4 — Tools
Tools | Tool buying tips | Minimum tools for ATV service | Advanced list of basic tools | Specialty tools (useful for all motorized vehicles) | ATV-specific tools | Chemicals | Working facilities

Chapter 5 — Safety
Age group recommendations | Safety materials and training | Safety gear | Pre-ride safety inspection | Safe operating practices | Tread lightly | Workshop safety

Chapter 6 — Accessories
Covers | Racks | Lighting | Winches | Plows | Hitches | Carts/trailers | Brush guards/bumpers

Chapter 7 — Brake Systems
General information | Drum brakes - general info | Disc brakes - general info | Hydraulic disc brake operation | Hydraulic disc brakes - caliper types | Brake fluid - general info | Brake inspection and service

Chapter 8 — Fuel and Exhaust Systems
General info | Air cleaner - filter element and drain tube cleaning | Fuel tank | Exhaust system - inspection and spark arrester cleaning | Carburetor - general info | Carburetor maintenance | Carburetor overhaul

Chapter 9 — Suspension, Steering and Frame
General info | Front suspension (three-wheelers) - construction and operation | Front suspension (four-wheelers) - construction and operation | Steering (three-wheelers) construction and operation | Steering (four-wheelers) construction and operation | Rear suspension - construction and operation | Rising rate suspension | Oil-damped coil spring/shock absorber units | Spring preload adjustment | Frame - general info

Chapter 10 — Electrical System
General info | Electrical troubleshooting | Battery - inspection and maintenance | Battery - charging | Fuses - check and replacement | Lighting system (battery-equipped models) - check | Bulb replacement | Headlight aim - check and adjustment | Taillight and brake light bulbs - replacement | Starter motor - construction and operation | Starter solenoids | Starter motor - overhaul | Starting circuits | Charging systems - general info | Flywheel generators and alternators - construction and operation | Charging system (battery equipped models) - testing | Ignition systems - construction and operation | Spark plug - replacement | Ignition system - check

Chapter 11 — Tires and Wheels
Tire and wheel sizes | Tire designs | Tire inflation | Wheel removal and installation | Tire mounting and dismounting | Tire inspection

Chapter 12 — Seats
Seat removal and installation | Seat care

Chapter 13 — Engine Maintenance
Engine oil | Engine oil filter | Engine air filter | Valve lash adjustment | Camshaft chain tension adjustment | Spark plug installation

Chapter 14 — Clutch, Transmission, and Final Drive
Clutches - general info | Centrifugal clutch - construction and operation | Centrifugal clutch - inspection and service | Multi-plate clutch - construction and operation | Multi-plate clutch inspection and service | Release mechanisms | Transmission - general info | Constant mesh transmission - construction and operation | Transmission - inspection and service | Final drive - general info

Chapter 15 — Troubleshooting
Engine starting | Clutch adjustment | Brakes | Rear axles | Steering/handling

Chapter 16 — Cleaning Your ATV
Cleaning materials | Washing/cleaning | Polishing/protecting

Chapter 17 — Storing Your ATV
Engine | Fuel system | Frame, cables, atc. | Battery | Tires | Covers | Bug- and mouse-proofing the ATV

Chapter 18 — Transporting Your ATV
Loading into a truck, van or trailer | Securing the ATV