DT400 Dirtbike Review Specs And Value

Yamaha DT400 Dirtbike

This new big-bore 400cc enduro was a hit with test riders. Go almost anywhere, do almost anything, and do it quickly! The DT1 250 had grown in size, first to 360, then to 400, and was now a very seductive machine.

The oversquare single-cylinder two-stroke could tackle a dune in the Mojave Desert, climb gnarly trails high in the Rocky Mountains, or hare along old logging roads in Maine, weighing less than 300 pounds and producing equal amounts of horsepower and torque.

These magazine riders were well-versed in the art of pinning the throttle fore and aft, making full use of the available power at all times. When it came to cruising along country roads, however, the 400's engine was not as smooth as many relaxed riders would have preferred—good for the hurly-burly of competition or the adrenaline-seeking individual off on his own, but not so comfortable for the commuter crowd.

DT400 Dirtbike Review Specs And Value

Let's start at the beginning, with the excellent DT1 250 from 1968. The Japanese had finally realized that there was a distinct "American" market that did not exist in Japan or Europe—and that market was made up of riders who wanted to take advantage of our vast publicly owned wilderness while maintaining a moderate level of adrenaline. The erroneously dubbed "street scramblers" were simply unsuitable, being far too street-oriented and far from scramblerish. The vast expanses of uninhabited land are one of the true blessings of our great land, and all that was required was a properly set-up motorcycle to enjoy the tens of thousands of miles of dirt roads and trails... A large gas tank was also very useful.

The DT1 was a fantastic motorcycle right out of the box, thanks to its two-stroke piston-port single with five ports, which provided the low-end grunt that play-bikers craved. Yamaha realized there was a significant difference between a race-winning machine and a machine that a noncompetitive rider would enjoy.

This unitized engine was bolted into a cradle frame with a double loop, which was plenty strong enough to handle the claimed 22 horsepower. It was a lot of fun without being too demanding. A Genuine Yamaha Tuning kit with a new cylinder, piston, expansion chamber, and other parts was also available in case someone wanted to race it.

They were so popular that dealers couldn't keep them in stock. Racers were quick to snap up the competitive MX and YZ models that followed. The smaller 125cc AT1 Enduro followed soon after, as did the larger 351cc RT1 360 Enduro with a bore of 80mm and a stroke of 70mm, which debuted in 1970. The RT1 was then modified and reintroduced as the DT360A Enduro in 1974, with Yamaha marketing executives realizing that the original DT1 250's success had given those DT letters value. To give it sportier handling and more power, the DT360A used a lot of MX parts, including the chassis. The reed-valve induction system and CDI ignition were also new, eliminating the often-annoying points.

However, the DT360A was only available for a year, as Yamaha quickly realized that there was not enough differentiation from the previous RT—and lo and behold, in 1975, the DT400B appeared, with the 360A bore out to 85mm for a total displacement of 397cc. It was crowned with a new head with radial finning that was very sexy. The Mikuni carburetor was 32mm in diameter, and combined with the reed valves, the engine was thirsty, getting only 30 mpg or less when cruising down a sand wash—and the gas tank was only 2.4 gallons. Even though the automatic lubrication oil tank held 1.6 quarts and was good for two full gas tanks, this severely limited the range.

The primary power was routed through helical gears to the multiplate clutch, which was then routed to the five-speed transmission. The dyno measured almost 24 horsepower at 5,500 rpm and 24 lb-ft of torque at 5,000 rpm at the rear wheel. For the experienced rider, 5,000 rpm was the sweet spot, and in fifth gear, the bike could easily exceed 80 mph on a straight stretch of road.

DT400 Dirtbike Review Specs And Value

With a 30 degree rake and 5.1 inch of trail, however, such speeds were not sustained for long. The fork had three stages of progressive springing, and the rear Thermo-Flow shocks had double springs and remote reservoirs. The front tire was a 3.00 x 21 Dunlop Trials, and the back was a 4.00 x 18...though a 4.50 knobby could be squeezed in. The single-leading-shoe brakes were designed for dirt riding, and attempting a quick, unplanned stop on the pavement could cause mild panic. The vehicle had a 56-inch wheelbase.

The most difficult part was getting the bike started. A 400cc single two-stroke engine is a big one to start, and while the automatic compression release worked great, the CDI could be a pain to start first thing in the morning. A rider could also expend a lot of energy kicking when the engine was hot. As one publication put it, "there was no sure-fire drill to follow," and "starting was unpredictable."

The DT400 was a little jerky on the road once it was running, as the engine didn't like constant throttle—unless it was wide open all the time. Dealers thought these bikes would sell in the thousands, even at $1,370, at first glance. The non-current 1975 models, on the other hand, were on sale for $948 a year later. Despite lower-than-expected sales, Yamaha continued to improve the DT400, introducing a mono-shocker rear suspension in 1977.