Yamaha DT400 Enduro Dirt Bike (Specs and Review)

The ’70s was a critical time for Enduro-style motorbikes – including the Yamaha DT400. Despite the ingenuity from manufacturers, the impending decline of 2-strokes took a toll on the appeal of motorcycles. Had it not been for its praiseworthy qualities, the DT400 would have been long lost in the said battle.

The Yamaha DT400 was an Enduro-style dual-sport wheeler produced from 1975 to 1979. An upgraded version of the DT360A, this dirt bike sported an MX-inspired frame and suspension, classic styling, and an 87-mph top speed rating. It was better suited off-road than it was on-pavement.

You would think that this dirt-road orientation was a welcome attribute. Unfortunately, the Yamaha DT400 adapts better to dirt roads than paddocks, which some riders consider a drawback. Thankfully, this notion has changed over the years, as more and more off-roaders make sense of the true capabilities of this retro-styled wheeler.

About the Yamaha DT400

The Yamaha DT400 is the largest displacement in the final iteration of the Yamaha DT product line. It is another spin-off of the 1968 DT-1 Enduro – the groundbreaking two-wheeler that initiated the dual-sport niche for Yamaha. The bike launched almost simultaneously with the DT250 series to provide consumers with more options for dual-purpose, off-road-worthy motorcycles.

Despite earning the moniker, “the best big-bore Enduro around” during its heyday, the Yamaha DT 400 was also infamously referred to as “yellow, fat, and holes pistons on a constant basis” – which was mainly due to its 2nd-year iteration. 1976 was a particularly futile year for the two-wheeler, as Yamaha’s efforts to make the bike both user- and environment-friendly resulted in an engine design that did neither.

Several factors contributed to the pig-like nature of the Enduro-style bike. The use of an oddly-shaped squish band around the cylinder head and a 30-mm Mikuni carb (view on Amazon) lacking in size caused the DT400 to detonate when warm and hole pistons on a whim. Moreover, its engine’s added weight brought about by its Autolube pump, heavy castings, and counterbalancers did not help improve either the motor’s functionality or the bike’s overall reputation.

But not everything was lost with the DT400. Despite its shortcomings, it is still well-respected as a dirt bike and dual-sport wheeler. After all, the two-wheeler is popularly referred to as “a wolf in sheep’s clothing” because of the tremendous power hiding behind its sleek, stylish lines. Like all other motorcycles, the Yamaha DT 400 is imperfect (a fact most veterans can agree to). But scrambler-oriented modifications and a few other tweaks here and there are guaranteed to unleash the bike’s full potential.

1975 Yamaha DT400 Specs & Features (DT400B Model)

Engine

The DT400 has a single-cylinder, 2-stroke power mill with a 28-mm Mikuni carburetor (other online sources mention 32 mm) and reed-valve intake system feeding the engine its required air-fuel mixture. This unique torque induction lends to a Yamaha DT400 horsepower of 21 – 24 hp (15.3 – 17.7 kW) @ 5,600 RPM and improved power delivery at low RPMs. The powerplant is mated to an air cooling system and has a bore-stroke ratio of 85 x 70mm, a 6.4:1 compression ratio, and a piston displacement of 397 cm³ (24.22 in³).

Fuel & Lubrication

Fuel travels via a membrane-type camshaft valvetrain configuration, which renders a decent (unofficial) gas mileage of 30 – 45 mpg (5.2 – 7.8 L/100 km) depending on riding conditions. Tank capacity is 9 L (2.38 US gallons) of unleaded gasoline with a minimum PON 87/RON 91 rating. Fuel variants containing less than 5% MTBE (Methyl Tertiary Butyl Ether), 10% ethanol, or 5% methanol are preferred, although there are stern recommendations against methanol-containing fuel.

Lube-wise, the DT400 uses the Yamaha-exclusive Autolube feature that automatically adjusts oil flow into the engine load. Recommended oil capacity for this lubrication system is 1.1 L (1.2 US quarts) of Yamalube SAE 10W-30 2-stroke oil or its equivalent, with a minimum SJ API grade meeting JASO T903 MA/MB standards. 1975 production models had a slightly higher engine oil capacity at 1.5 L (1.6 US quarts). Other manual-specified viscosity grades are permitted, following ambient temperature.

Drivetrain

A 5-speed, constant-mesh manual transmission mated to helical gears, and a wet multi-disc clutch assembly delivers power to the wheels. A Daido DID520DS chain (with 103 links + joint) handles wheel spin. The dirt bike’s 5-speed gearbox yields a Yamaha DT400 top speed of 84.5 – 87 mph (136 – 140 km/h) and a maximum torque of Nm (3.8 kgf-m, 27.5 ft-lb) @ 5,000 RPM. It idles at 1,400 – 1,500 RPM for units sold in Europe and 1,300 – 1,400 RPM for other markets.

Ignition

An electronic CDI (Capacitor Discharge Ignition) and primary kick-start system bring the Yamaha DT400 to life. The CDI system eliminated problems with Contact Breaker Point ignition systems present in older Yamaha DT iterations, making the two-wheeler more dependable and less troublesome when servicing. All production models require an NGK B8ES spark plug with a gap of 0.7 – 0.9 mm (0.028 – 0.035 inches) and 25 Nm (2.5 kgf-m, 18 ft-lb) torque specification.

As for battery, 1975-1976 models used 4Ah/(10 HR) 6N4B-2A-3 battery formats, while 1977-1979 models had 6Ah/(10 HR) 6N6-3B-1 batteries – similar to the DT250 series. These formats differed in dimensions and amperage and were non-interchangeable. The 6N4B-2A-3 battery (view on Amazon) was 102 x 48 x 96mm, and the latter was 99 x 57 x 111mm.

Tires & Brakes

Tube-type, 4-ply Dunlop® Trials measuring 3.00-21, 80/100-21 (view on Amazon) at the front and 4.00-18, 120/100-18 at the back are mounted on spoke wheels. Recommended cold-tire pressure for these factory tires are 127.5 kPa (1.3 kgf/cm², 18.5 psi – front) and 147 kPa (1.5 kgf/cm², 21 psi – rear) for normal riding but can adjust up to 176.5 kPa (1.8 kgf/cm², 25.6 psi) for high-speed riding or when driving with a passenger. Expanding brakes at the front and rear complete the DT400 tire-and-wheel assembly and provide the bike with its halting power.

Suspension

Enclosed in a motocross-type cradle frame are front telescopic forks and a rear swingarm with Thermo-Flow shocks that prevent overheating and damping inefficiency. Each suspension setup provides a respective wheel travel comparative to the DT250. In 1977, Yamaha introduced a nitrogen-charged rear mono-shock with softer spring rates, further supporting the bike’s superb handling and improving its cornering and off-road performance. These upgrades worked perfectly with the DT400’s 55.5-inch wheelbase, 2-meter turning radius, and 8.7-inch road clearance.

Dimensions & Capacities

Overall dimensions are 2,180 x 870 x 1,140 mm (85.8 x 34.3 x 44.9 inches – L x W x H). Little to no difference is observed in the measurements of later-year releases – although earlier DT400s were slightly smaller than the DT250 and DT400D. Wet and dry masses are heavier compared to its 250-cc namesake. The bike’s dry weight is 124 Kg (272 lbs.), while its curb weight is 141 Kg (310.9 lbs.).

Exterior

The Yamaha DT400 had the same vintage styling as its smaller-displacement cousins and was available in Blue, Red, and Competition Yellow. These bodypaint options work well with the black-painted chassis and large round headlights that provide excellent illumination (especially for late-night riding). Standard features include turn indicators, a comfortable two-up saddle seat, serrated footpegs, and upward angled instrumentation. Raised front/rear fenders and a side-mounted exhaust system add to the dirt bike’s ruggedness.

Yamaha DT400: Pros and Cons

Pros

• On a straightaway in 5th gear, the DT400 could easily exceed 80 mph (130 km/h).
• Its leading-shoe brakes provided the bike with excellent stopping power in the dirt.
• Large cooling fins covered the engine head and cylinder and helped dissipate engine heat.
• Like the DT250, the Yamaha DT 400 boasts dual pieces such as brake levers, instrumentation, and a duplex frame.
• A contoured saddle seat comfortably accommodates two riders, including the driver.
• DT400 owners need not worry about aftermarket support.
• Stock parts are interchangeable with YZ250 components (of course, slight modifications are involved).
• Its charming, vintage styling greatly resembles other Yamaha DT iterations.

Cons

• The pairing of the Autolube and the 9-liter fuel tank is a grave mismatch – the tank capacity is quite restrictive, while the oil capacity is suitable for two full tanks of gasoline.
• Despite having an automatic compression release, the motorbike can prove difficult to cold-start due to its hefty engine.
• Yamaha DT400s were fuel guzzlers due to their carburetor size and relatively small fuel tank capacity.
• Upgrading headlights, enhancing light distribution, and turning the motorbike into a road-legal ride required converting the two-wheeler’s wiring and electrical components to 12V.
• Low- and mid-range pull-aside, the DT400 does not inspire a lot of confidence when traversing dirt and other technical terrain.

Yamaha DT400 Price

Original list prices for the Yamaha DT400 ranged between $948 and $1,370 (or approximately $4,645 to $7,100 if valued today). That price increase is just a little over $400 over five years. Compared to its current worth in the used-bike market, the incoming model year of the DT400 did not sell very well. This pushed Yamaha to drastically lower the bike’s MSRP on its 2nd year onward.

Ironically, the dual-sport wheeler (pre-loved) seems to keep its value quite well. Auction listings and Nada Guides data price the vintage motocrosser between $730 and $4,230. Similarly, bidding can range from $1,500 to $2,125 on eBay and may sell for similar price ranges on other trading platforms. Secondhand units below $2,000 may require minor touch-ups to the paint and a complete front-and-rear tire replacement. Also, expect these bikes to have a few nicks and scratches. Other than that, they should be in good working condition.

About Yamaha

Yamaha Motor Company Ltd. took nearly 70 years from its founding before venturing into the automotive world. In 1955, the Japanese manufacturer decided to part ways with its parent company to begin its journey in the ATV and motorcycling industries. Not long after, Yamaha successfully established itself as a game-changer in these fields with groundbreaking products like the Yamaha DT400. The firm upholds its legacy with its unrivaled water vehicle sales and innovations in multiple industries.

Conclusion – Yamaha DT 400 Review

Some say the Yamaha DT400 is redundant when put next to the DT250. Although this may have some truth, it does not undermine the bike’s prowess. It is practically a prototype of 500-cc dual-sport motorcycles – without which the near-perfect, well-balanced traits of its class would not have materialized. If you are looking for a nostalgic dirt bike with qualities befitting daily commute as they do the International Six Days Trial, then look no further than the Yamaha DT400!