This Clymer DIY repair and service manual, covers 1985-1986 Honda ATC250R, TRX250R, and 1986-1989 Fourtrax 250R models.
Book Excerpt: 1985-1989 Honda TRX250R, Fourtrax 250R, ATC250R ATV Repair Manual FUEL AND EXHAUST SYSTEMS

The fuel system consists of the fuel tank, the shutoff valve, a single carburetor and an air filter. There are 2 different carburetors used among the various models. The exhaust system consists of an exhaust chamber, a muffler and a spark arrester. This chapter includes service procedures for all parts of the fuel system and exhaust system. Air filter service is covered in Chapter Three. Carburetor specifications are covered in Table 1. Tables 1-7 are located at the end of this chapter. CARBURETOR OPERATION For proper operation a gasoline engine must be supplied with fuel and air mixed in proper proportions by weight. A mixture in which there is an excess of fuel is said to be rich. A lean mixture is one which contains insufficient fuel. A properly adjusted carburetor supplies the proper mixture to the engine under all operating conditions.

READING SPARK PLUGS

Much information about engine and spark plug performance can be determined by careful examination of the spark plug. This information is more valid after performing the following steps.

1. Ride the ATV a short distance at full throttle in any gear.
2. Turn the engine kill switch to the OFF position before closing the throttle and simultaneously shift to NEUTRAL. Coast and brake to a stop.
3. Remove the spark plug and examine it. Compare it to Figure 72.
4. If the plug is defective, replace it. If its condition indicates other engine problems, the engine cannot be properly tuned until repairs are made.

IGNITION TIMING

The engine is equipped with a capacitor discharge ignition system (CDI). This system uses no breaker points, and there are no means of adjusting ignition timing. Incorrect ignition timing can cause a drastic loss of engine performance and efficiency. It may also cause overheating.

Subject: 1985, 1986, 1987, 1988, 1989 Honda ATC250R, TRX250R, Fourtrax 250R service, maintenance, repair. ISBN-10: 0892875402 ISBN-13: | 9780892875405 | Clymer M348