Suzuki GSX 400F Impulse

HAVING WAITED for the right moment, the latest 400cc naked 'retrostyle' bike, Suzuki's Impulse, has been launched here in Japan.

The first Impulse appeared in Japan back in 1982. Based on the GSX400F, that bike had a Yoshimura 4:1 exhaust system, aluminium swing-arm and adjustable rear shocks. The second Impulse came out in 1986 with, I think, rather odd styling by Hans Moult, the father of Katana.

Unlike previous Impulses and the other Suzuki roadsters such as the Katana and GSF400 Bandit, the third generation Impulse has rather conventional styling. Nothing surprises at all. The only thing that looks any different from any of the others is the tank. The angular shape makes it look as if it has been made of cardboard, but Suzuki says it emphasises its muscular style.

People's attitude to bikes is changing. There is now less emphasis on the maximum speed and power of a machine. Instead power delivery is becoming the most important factor; how well the engine and chassis blend and how much you can enjoy the bike in any situation. Thanks to the power restrictions in Japan (400cc bikes are restricted to 53bhp), the manufacturers have realised they can make more interesting motorbikes with less power. Suzuki reckons the Impulse is the most sparkling 400 naked bike ever.

I rode the bike in Tokyo for a day and the most remarkable thing I noticed at first was its massive low-down torque. I started the engine, clicked into gear, released the clutch lever and the Impulse started moving very smoothly and reassuringly — not something you expect from a 400cc bike.

The liquid-cooled, transverse-four engine with a 52mm x 47mm bore and stroke is from the Katana 400 which was already quite powerful in the low to middle reaches.

Suzuki has given the engine smaller 29mm carbs to improve the throttle response and deliver even stronger torque low down. The bigger seven-litre airbox with larger intake ports is a further improvement.

In an awful traffic jam in Shinjyuku, where many skyscrapers, including the Tokyo metropolitan building and many sex shops are, the flexible engine made the bike easy to ride and overtaking buses, taxis and pizza-delivery bikes was simple. To ride through a traffic jam on a bike, the engine should work without lagging and have enough torque at any revs. The Impulse achieves this almost perfectly.

In Tokyo there is a highway called Suto-Kousoku. This has a central circuit and many radial roads extending to the outskirts of of the city (the toll costs 700 Yen for a motorbike - or about £4.50). I went around the central circuit on the Impulse in the morning before the mad rush hour and found the chassis worked quite well with the powerful engine. It has a traditional double-cradle frame, 41mm front forks and an aluminium swing-arm which is an 'H' shape in cross section for added strength. The chassis is not especially outstanding, but it is stiff enough and has reasonable flexibility. The brakes are superb: two 290mm floating discs with twin-piston calipers at the front and a 250mm disc with opposed piston caliper at the rear. They manage to stop the bike quickly before you crash into a taxi which suddenly turns and stops to collect customers. The handling has no vices and copes easily with Tokyo riding.

The Impulse is set to be competing against other nakeds in Japan such as the Kawasaki ZRX, Zephyr 400, Honda CB400SF, Yamaha XJR400, Suzuki Katana 400 and Bandit 400. It's being said here that Japanese motorcyclists are in the middle of a naked boom, but my feeling is that it isn't just a boom. The naked bike is becoming Japan's standard after having a racer-replica boom. In other words, we are getting 'back to basics'. Basic can be anything, like a pair of jeans can be worn in both a formal and an informal way. The Impulse might not be the most stylish of bikes, but it's certainly one of the toughest.