2003 Honda 400EX SporTrax (Specs and Review)

The 2003 Honda 400EX (a.okay.a. TRX400EX or SporTrax) has grow to be a family title amongst hobbyists and fans. Its recognition ought to be no shock because the 400-cc SporTrax has at all times been considered one of the succesful and enjoyable quads round. Ruggedly aesthetic and stark, this 4×4 launched pure-sport 4-strokes into the ATV panorama and offered shoppers thrills and an entire lot extra – as you’ll quickly uncover on this information.

The 2003 Honda 400EX (in any other case generally known as SporTrax) hails from the sport-ATV lineup that signaled the renaissance of the game using phase. That includes an XR400R-adopted engine, 72-mph top-speed ranking, and Professional-Hyperlink rear suspension, it has grow to be a crowd favourite amongst sport-rec, 4-stroke quads.

Simplicity, versatility, and pure-sport ergonomics solely type half and parcel of the 2003 Honda 400EX’ key promoting factors. Proceed studying in regards to the specs, options, and lowlights of this sport using bigwig on this article to be taught extra.

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Concerning the 2003 Honda TRX 400EX

The 2003 Honda 400EX is the fifth installment of the Sportrax lineup since its inception in 1999. A sport-oriented machine right down to its core, the SporTrax’s dedication to the revival of the game using phase turned a rallying level for its loyal followers. Consequently, it additionally led to the Honda 400EX making a reputation for itself as a motocross-worthy four-wheeler.

Successful the Baja 1000 recent out of the crate is immensely accountable for this exceptional feat. The machine wouldn’t have been capable of obtain this had it not been for its XR400R-inspired engine and different race-ready elements. Finally, Honda needed the ’03 mannequin to dominate MX/GNCC arenas alongside highly effective 2-stroke contenders already gracing the sport-ATV scene. However on account of setbacks in general design and shortage of tech and have upgrades, the machine was ultimately resigned to being a critical path tamer.

2003 Honda 400EX Specs & Options


The 2003 Honda 400EX is delivered to life by an air-cooled, single-cylinder 4-stroke engine. Piston displacement is 397-cm3 (24.23 in3), the bore-stroke ratio is 85 × 70 mm (3.35 × 2.76 inches), and the compression ratio is 9.1:1. This racing-inclined energy mill equips a Radial 4-Valve Combustion Chamber and a 38-mm piston valve with an accelerator pump. The 38-mm carb mates to oiled, urethane-foam air filtration and dry-sump lubrication and handles air-fuel combination.

Given the SporTrax engine was adopted from the XR400R, its configuration will naturally lend to a 2003 Honda 400EX high velocity of 65 – 72 mph (105 – 116 km/h) and a 28 RWHP (20.59 kW) horsepower. General, the quad’s powerplant is fairly strong. Nonetheless, you’ll need to regulate the carburetor for high-altitude using above 3,000 toes or 1,000 meters.

Gas & Lubrication

It has a 2.64 US gallon gas tank capability. Utilizing gas with the suitable octane ranking is prime and reduces (if not eliminates) engine pinging or spark knock. Stopping contaminants similar to mud, dust, or water from getting contained in the tank additionally helps.

Engine pinging outcomes from the air and gas combination inside an engine cylinder igniting incorrectly. Therefore, count on slight pinging when using uphill or underneath heavy load, as these circumstances can probably trigger mistimed ignition. Nonetheless, consulting knowledgeable mechanic or instantly altering gas manufacturers is strongly suggested if pinging happens at sustained speeds or underneath regular using circumstances.

As for engine oil, capability is 1.7 liters/1.8 US quarts (after draining) or 2.2 liters/2.3 US quarts (at disassembly) of SAE 10W-40 Professional Honda GN4/HP4 motor oil or its equal. Different viscosity grades – SAE 5W, 10W-30, 20W-40, or 20W-50 – are permitted to be used following ambient temperature. For wonderful lubrication and unaffected clutch efficiency, use oil variants with a minimal API grade of SJ+ assembly JASO T903 MA/MB requirements. Chorus from utilizing non-detergent, vegetable, castor-based racing, or engine oils with graphite or molybdenum components.


Energy travels to the bottom through a 5-speed constant-mesh transmission and a cable-operated, moist, multi-plate clutch meeting (with a 1-N-2-3-4-5 gearshift sequence) sans reverse. An RK520 SMOZ10S or DID520V6 O-ring sealed chain (96 or 120 hyperlinks + joint) – replaceable by a DID 520ERT3120RB 520 ERT3 Series Exclusive Racing Chain (view on Amazon) – handles wheel spin. A gear-driven counter-balancer reduces undesirable engine vibration, making for easy maneuverability no matter terrain issue. Plus, its fording depth restrict of 10 inches (25.4 cm) permits the quad to traverse shallow water crossings with ease.

Major Discount Ratio 2.826 (23/65)
Last Discount Ratio 2.533 (15/38)
Transmission Gear Ratio – I 2.917 (12/35)
Transmission Gear Ratio – II 1.938 (16/31)
Transmission Gear Ratio – III 1.474 (19/28)
Transmission Gear Ratio – IV 1.182 (22/26)
Transmission Gear Ratio – V 1.000 (26/26)


Placement of a lot of the controls – such because the clutch and parking brake levers, begin button, headlight/dimmer/engine cease switches – are positioned on the left handgrip and has been this fashion for almost all of the 2003 Honda 400EX yr fashions. The gas valve, gear pedal, and choke lever are on the identical facet of the engine. Throttle levers, entrance brake fluid reservoir, entrance brake, and clutch lever are on the best handgrip. The impartial indicator lamp and ignition swap stay on the middle console, whereas the rear brake fluid reservoir and operator foot peg are on the best facet of the 4×4.


An ICM (or Ignition Management Module) and electrical beginning system with an idle velocity of 1,400 ± 100 RPM brings the ’03 SporTrax to life. A single-phase (SCR shorted, full-wave) alternator with a rated output of 0.147 kW @ 5,000 RPM serves as its charging system.

It makes use of a maintenance-free 12V 8Ah/(10 HR) YTX9-BS battery with dimensions of 150 x 87 x 105 mm for powering digital equipment. It additionally requires a Nippon Denso X24GPR-U or NGK DPR8Z spark plug with a 0.024–0.028 inch hole and torque spec of 1/8 – 1/4 flip (outdated plugs) or 1/2 flip (new plugs) after the plug seats. For prolonged, high-speed using, swap to an NGK DPR9Z or Nippon Denso X27GPR-U spark plug as a substitute.

Tires & Brakes

Entrance 22 x 7-10 M/R 101 and rear 20 x 10-9 M/R 501 Ohtsu radials (every with a 4/110 bolt sample) mount on metal or aluminum wheels. These knobbies pair with all-wheel-drive triple hydraulic discs (174-mm twin entrance discs and a single 220-mm rear disc) with twin brake calipers, offering the 4×4 a 70:30 p.c ratio of its stopping energy. Entrance wheels are 10×5.5 AT mags, whereas rear ones are on 9×8.0 AT rims (view on Amazon). Aftermarket tires like Maxxis Razr 4-Ply Sport Tires (view on Amazon) are wonderful replacements for inventory rubber in case of wear and tear or harm.

Yellow 2003 Honda 400EX ATV

Entrance and rear cold-tire stress ought to be 27 kPa. Relying on the terrain kind, airing down or inflating tires throughout the vary of 23 kPa to 31 kPa is permitted. Common tire tread inspection is essential, as a depth of no less than 0.1875 inches (4.0 mm) warrants fast tire substitute.


Enclosed in a double-cradle metal body (6.5° caster angle, 28-mm path) are unbiased, entrance double-wishbone with 5-way preload-adjustable shocks and a Professional-Hyperlink rear swingarm with a completely adjustable Showa mono-shock. Every setup gives a respective wheel journey of 209 mm/8.2 inches and 230 mm/9.1 inches. The 48.4-inch/1,230-mm wheelbase, 4.3-inch/110-mm floor clearance, and three.2-meter/10.5-feet turning radius stay unchanged as in previous-year fashions. All in all, the machine’s suspension elements make for diminished unsprung weight, tighter cornering, and improved traction.


General dimensions of the 2003 Honda TRX400EX are 72.2×45.3×43.7 inches. Seat top conveniently accommodates medium-built to taller riders at 810 mm/31.9 inches and is ideal for ripping by flat surfaces. The GVWR estimate is at 635 lbs., together with the utmost load capability of 243 lbs., the curb weight of 392 lbs., and a full fuel tank.


The ’03 SporTrax was one of many earlier fashions that had but to obtain Crew Honda-inspired graphics. The general styling is simplistic and nice for personalization whereas strong sufficient to safeguard the engine and different inner elements from the weather. The entrance cowl and manufacturing unit fenders can profit from racing decals and aftermarket 2003 Honda 400EX components so as to add a contact of aggressiveness to the quad.

2003 Honda 400EX plastics have been accessible in purple and yellow, with body-matching, high-clearance fenders, and heavy-duty urethane skid plates that defend the wheeler’s underside and rear brake-disc/sprocket. You’ll be able to preserve the physique panels as damage-free as potential by spray cleansing them with operating water and gentle detergent. Chorus from utilizing an influence hose, as it could actually trigger abrasions and result in corrosion.

2003 Honda 400EX Worth

The 2003 Honda 400EX retained its listing worth of $5,699, cheaper by $400 towards the 2000 MSRP. This aggressive pricing gave it an edge over its same-class counterparts. Moreover, it was a smart resolution on Honda’s half, as just about nothing has modified within the machine’s framework and general design. Like manufacturing fashions from the earlier yr, the ’03 SporTrax solely provided customary trims – maybe, a way for the Japanese agency to maintain the quad’s retail pricing in examine.

As for resale values, costs vary from $1,805 to $2,375 per Nada Guides knowledge. About the identical worth vary – from $978 to $3,000 – exhibits in public sale listings, Craigslist, and different dealer websites. Most of those pre-owned models are in respectable, operating situation, and incessantly bought within the UK, California, Texas, and North Carolina. Close to-mint quads would naturally fall on the upper finish of the worth spectrum and are available outfitted with performance-enhancing add-ons, elevating the common resale worth by no less than $500.

Honda 400EX Beginning Situation

Bore will increase and gas/electrical system issues apart, a no-start concern is innate with the ’03 Honda SporTrax. And often, the very first thing you’ll discover is your starter motor trying to show your engine over with none luck. When this occurs, examine the spark plug tightness, engine cease switches, and battery whereas making certain the latter has a full cost. Likewise, decide if any bore modification was executed and if this was carried out appropriately. If these elements try, chances are you’ll start inspecting different elements to pinpoint if the perpetrator is engine flooding, gas hunger, or another kind of breakdown.

Different issues to be careful for are head gasket leaks, flimsy swingarm, overheating, and intermittent stalling. The clutch and gearbox are reportedly problematic – particularly for closely modded quads or these used for racing purposes. Inventory tires are additionally not as puncture or damage-resistant as house owners would have preferred. Most of the time, these points stem from driving habits and don’t essentially imply the 4×4 falling brief on sturdiness. Fortunately, your service guide gives related info on the way to tackle these hiccups.

About Honda

Honda Motor Firm Ltd. is a Japanese conglomerate identified worldwide for its ingenuity in automotive design and a dominant power within the ATV and motorcycling industries. Established in 1937 as Tōkai Seiki or Japanese Sea Precision Machine Firm, Honda started as Toyota’s provider of mass-produced piston rings. Since then, the Japanese agency has come a good distance, diversifying its product choices to incorporate surplus engines, motorized bicycles, mini pickup vehicles, and ultimately venturing into ATVs just like the 2003 Honda 400EX.

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Conclusion – 2003 Honda 400EX Assessment

It took one other two years for Honda to offer the 2003 Honda 400EX suspension upgrades. However even then, the four-wheeled machine nonetheless was not on the receiving finish of GNCC-worthy modifications. Most elderly-timers might imagine the corporate’s present of restraint did it extra hurt than good. However for fans with a clearer understanding of the long run, the quad’s starkness definitely gave us, house owners, extra freedom to make the automobile their very own. Extremely-skilled operators and informal riders can agree that the power to customise a machine can dramatically enhance one’s using expertise – whether or not on wooded trails or hard-packed roads.

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