Honda ATC250R
The ATC250R is a high-performance ATV produced by Honda from 1981 to 1986. Early models (1981-1984) used an air-cooled, 248 cc single-cylinder two-stroke engine. Fuel was fed through a 27 mm (1981-1982) or 30 mm (1983-1984) round-slide carburetor. Power was accessed through a close-ratio five-speed transmission with a manual clutch. Later models (1985-1986) used a liquid-cooled, 246 cc single-cylinder two-stroke engine with a 34 mm round (1985) or flat (1986) slide carburetor. The biggest engine downfall was the lack of a power valve. The 85-86 models were upgraded with a close-ratio six speed transmission again with a manual clutch.
All model years were fully suspended and adjustable, using air-assisted front forks and a single, remote reservoir gas-charged rear shock. 1981-1982 models offered 6.7 inches of front suspension travel and 4.3 inches in the rear, 1983-1984 offered 8.7 inches in front and 8.1 inches rear, while 1985-1986 gave 9.8 inches of travel. All model years also used a gear-driven counter-balancer to reduce engine vibration. Dual disc brakes were used on all model years, with the exception of the 1981, which used a front disc and a rear drum.
The 1981 ATC250R marked a milestone in off-road history, as it was the first two-stroke ATV designed specifically for racing. While ATV racing was in its infancy, racers had to rely on Honda's ATC110 and ATC185 models on the racetrack. Both of these four-stroke models were sluggish and poorly suspended when compared to the 2-stroke ATC250R.
The 1983 ATC250R incorporated many improvements over the prior 1982 model, mainly with the introduction of Pro-Link suspension, folding foot pegs, a larger fuel tank, slightly longer travel suspension in front and rear, and other improvements.
The 1986 ATC250R was the last model year offered for sale in the United States, after an agreement between manufacturers and the Consumer Product Safety Commission to cease production on all 3-wheeled ATVs. This was the result of thousands of legal battles regarding safety issues and high accident rates.
The 1986 Honda TRX250R Fourtrax was the 4 wheeled brother of the ATC250R, with an engine that was virtually the same (with slightly less horsepower).
Honda also created three other machines of similar size for their HRC race team, but these were not production models. These machines are the ATC125R, ATC200R, ATC300R, ATC350R, ATC400R, ATC480R, and ATC500R. Of these machines, the ATC200R was most popular. Rumour has it that before the cease of production, Honda was building an ATC500R for production.
Engine Specifications
Engine type - Water-cooled 1985-1986, 2-stroke, single-cylinder
Bore & Stroke - 66 x 72 mm
Displacement - 248 cc for 1981-1984 or 246 cc for 1985 and 1986
Compression ratio - 8.0 to 1
Lubrication - fuel:oil mixture
Air filtration - foam element
Cylinder Bore - 66.020 - 66.040
Piston/cylinder clearance - 0.060 - 0.080
Piston Diameter - 65.94 - 65.96 mm
Pison pin bore - 18.007 - 18.013 mm
Piston pin outer diameter - 17.994 - 18.000 mm
Piston-to-piston pin clearance - .007 - .019 mm
Piston rings per piston compression - 2
Ring end gap - .20 - .40 mm
Ring side clearance - .045 - .075 mm
Connecting rod (sm end inner diameter) - 21.997 - 22.009 mm