Yamaha’s YZ400FR – bred from world championship MX success
In February 1978, after Motorcycle had acquired the services of Vic Eastwood for an exclusive test of Heikki Mikkola’s 1977 500cc world championship-winning Yamaha on which the YZ400FR was based, between them, Vic and Chris Myers wrote the following.
Vic Eastwood’s snap verdict after an afternoon’s ride on last year’s 500cc world championship-winning Yamaha was: “So smooth -- the power, the ride, the controls… everything is so smooth.”
The big Yam had started up willingly after a few drops of water had been cleared from the carb. Vic had a chat with Mikkola to check out the bike and then gingerly set off around the twisty, hilly course set in the middle of an apple orchard.
“The going was muddy and very slippery, but Vic soon gained confidence and speed -- he was obviously enjoying himself. Mikkola went out on his new bike a few minutes later and for a while the two circulated together, play racing.”
When Vic was eventually prised off the bike, which was so light he’d lifted the back wheel up off the ground with no trouble before even getting on to it, he said: “When I was riding the bike, I just wasn’t conscious of its weight at all. It must be right on the FIM weight limit, but what really struck me was just how easy it was to ride, with no vices at all. Joe Bloggs could jump on this and go well.
“The smoothness applies to the whole bike. Even the seat is goodness knows how thick – it’s so comfortable. The suspension makes it a tireless bike to ride, too, with 11 inches available at the front and the rear.”
The rear suspension was so good that Vic hardly noticed the bumps, but he found the front springing a bit hard (Mikkola’s mechanic did say that they’d put a harder set of springs in at the end of the last season).
“With adjustable damping in both directions and variable preload on the monoshock unit, the bike could be tuned to suit almost anyone and any circuit,” wrote Vic. “The Yamaha works men have obviously found the right set-up for Mikkola and it suited me too, but I stand by what I said when I rode the production bike -- I think it’s far safer for the average bloke to leave the settings alone.
“I found the rear suspension better than that on the production bike I rode last year. The works bike has more movement at the rear and it works very well. I can’t say that the massive alloy box section monoshock rear unit was any stiffer than the production tubular design, but this is clearly lighter.
“The front suspension I found about the same, but again I think the works version has more movement available.”
Like the production forks, the works forks could be pumped up with air to give a variable pre-load.
Once he’d become used to the bike, Vic Eastwood found the steering very precise, too. “It’d go wherever I wanted, no problems,” he said. “If I was going a little too fast in a bumpy rut it would just bounce out. I could just drift along feet-up a lot of the time and pick my way over the holes -the smooth engine power helped here.”
He found the engine’s power delivery much different from that of the 1977 production bike. “It’s so much smoother,” said Vic. “The power comes in smoothly right through the rev range. Just cog up and away you go, but on the other hand the production version is fiercer -- it comes on song and takes off.
“The smooth power makes the works bike so easy to ride, and it doesn’t do anything funny. Coming out of a corner in the right gear, you just open it up and blast away. The acceleration is great, and Mikkola always got great starts last year.
“The gearbox is smooth and precise, and once I got used to the bike I found that I could go around the whole course, hills and all, in third.”
While Eastwood found the rear brake superb, the front wasn’t as powerful and progressive as he would have liked. Although he stalled the motor a couple of times when locking up the rear wheel, all he had to do was take off the brake and it would pick up again.
“I’d say the compression ratio must be very low,” he added.
Vic found the Yamaha easy to start, and found the clutch super smooth as well. “It’s very light, tireless to use, and suited the motor perfectly,” he said. “All the controls came to hand easily. Mikkola and I are of similar build, although he might just be a little bit heavier, and nothing had to be altered to suit me. I just got on and away I went. “Everything about this bike was just right, and one little detail I liked particularly was the integral cover over the edge of the twist grip to keep out mud and dirt -- only a small thing, I know, but it shows just how much thought had gone into the preparation of the bike.” As a former development engineer and works rider, Vic was very impressed by Yamaha’s super smoothie. “There’s a lot to be said for a bike you can ride flat-out and under control,” he said. “Unfortunately you just can’t do that with a lot of motocrossers because they are just too fast. Yamaha has got it absolutely right. It’s a fantastic bike and it’s piloted by a fantastic rider. Put the two together and you’ve got the world championship -- right?”