SUZUKI SP/DR 370/400

This is the start of a series of articles about some of the bikes you will see at our events. In this article we are going to have a look at the Suzuki SP/DR400, an excellent low cost first step into classic scrambling.

The Suzuki SP/DR400 started life as the DR/SP370 as Suzuki hoped to cash in on the growing big-bore 4-stroke enduro bike market started by Yamaha with the XT500. The 370cc engine was then bored out to 400cc and Suzuki launched the SP/DR400. The format of the engine is the same with a two-valve single overhead cam layout and the same stroke as the 370. There are sight differences as the 400cc lump uses heavier crankcases but most parts are a direct swap between both versions. One problem with campaigning an SP/DR 370/400 is the availability of pistons as they have been discontinued by Suzuki.

Technical specifications
Value now (est): £800-1000
Power: 30bhp
Torque: 20ft-lb
Top speed 82mph
Dry weight: 136kg
Colours: Red, Yellow
Fuel: 8.6litres
Rake/trail: 29deg/146mm
Seat height: 790mm
Wheelbase: 1320mm
Engine capacity: 396cc air-cooled cc (88 x 65.2mm),
Engine type: single-cylinder SOHC four-stroke.
Fuel control: 36mm Mikuni CV carb.
Gearbox: 5 speed with multi plate wet clutch.
Chain final drive
Chassis: Tubular steel single down tube frame
Front suspension: 36mm telescopic forks
Rear suspension: Twin oil-damped rear shocks with adjustable preload Brakes: 150mm single leading shoe drum front and rear
Tyres: 300 x 21 front, 400 x 18 rear

We will now have a look at the SP400 ridden by William McMaw at our meetings. The bike is non standard in quite a few ways starting with the forks. The original forks were badly pitted and a replacement set proved hard to come by so the bike is using RM400 stanchions inside the original SP400 sliders. At the rear the bike uses a pair of 70's KONI shocks with home made rods.

The bike has been raced for around 6 seasons without any problems with the only rebuild of the engine occurring to make the move to the XT500 piston. While not on the level of a 490 Maico or a 500 Husqvarna the performance from the bike is excellent considering the cost of the machine. William reckons that the total cost to date after 6 seasons is still under £1000 including the modifications.
Enduro four strokes like this Suzuki provide a low cost stepping stone into classic scrambling so you can enjoy a day out without feeling too much pain in your wallet. All the more reason to get a bike and give classic scrambling a go!
Moving on the engine the original Mikuni CV style carburettor has been replaced with a 36mm Mikuni round slide and jetted to suit. The piston has been replaced with an XT500 10:1 high compression unit with the valve reliefs hand ground to suit the Suzuki valve pattern. The bottom of the barrel has been skimmed to raise compression and increase power output.