For anyone whose memory doesn’t go back that far, what I had bought was a four stroke single cylinder trail bike of 396cc (88 x 65.2mm bore & stroke) with a compression ratio of 9.2:1, fed by a Mikuni carb. Its two valves are actuated by a single overhead cam. Claimed power output is a modest 30hp and there are five gears.
It felt like a toy at first, being nearly 200lb lighter than my Yam XS650 at a claimed 280Ib dry, and much slimmer. Early experiments indicated nimble handling, reasonable acceleration with a top whack of just over 80mph, and good fuel economy.
The SP has never been my only bike (although there have been times when it was my only roadworthy one), so mileage has increased only gradually to its present level of 36000 miles. It has been used throughout as my commuting hack, a trip varying over the years from 9 to 75 miles daily. It is currently averaging about 500 miles a month, including the odd bit of trail riding. It is also my all weather transport and so it has made some longer journeys as well.
The best thing about the Suzuki is its amazing frugality, both on my money and my time, if used gently. Being a stingy sort of chap, I want it to last. I therefore make concessions to it, like not revving it hard when cold, changing the oil every 2000 miles (as opposed to the recommended 3000), and sitting back to enjoy the scenery rather than trying to arrive two minutes earlier. Used this way it will turn in 80mpg even when commuting and need next to no maintenance.
I should stress that I treat the Suzuki with consideration, or at least flatter myself that I do. Some UMG correspondents seem proud of neglecting their bikes, which I would have thought was asking for trouble, especially in winter. I will never be a keen DIY type, but look on the odd half hour’s maintenance as good insurance. Besides which, the bike is so easy to work on. Even I feel useful after doing a bit of work on it, and my mechanical aptitude is decidedly basic.
The fuel economy is helped by the engine's flexibility. First gear is hardly ever needed on the road, except for first thing in the morning or two up hill starts, and it will pull in top from about 25mph - provided you don't expect neck snapping acceleration. In fact, it’s best at low revs because despite being red-lined at 8000rpm, vibration comes in at around 5500rpm in a big way. I've fitted softer bar grips, which help a bit.
Parts life has been good, apart from the chain. The second clutch cable was fitted at 8000 miles, a-new tacho cable and silencer at 18000, and I've also added fork gaiters to protect the chrome and seals. It's on its third headlamp bulb and third battery, which being a puny 6V affair only costs £10. I also renew the plug annually, for peace of mind rather than out of any apparent need.
And, apart from a camchain, those are the only bits it’s had, I think, apart from a replacement side panel and a gear lever, which both vibrated off early in my ownership. Note to those about to buy their first big single - run around all bolts with a spanner at service time.
There was also the case of the collapsing motorcycle. I had just spent the weekend in Bristol, visiting my sister, and was riding home along the A4 to London, where I lived at the time. Unknown to me, the swinging arm spindle had sheared just behind its securing nut. The spindle naturally started to work its way free from the other side until it cleared the frame at the sheared end. At which point the arm and rear wheel slewed to one side.
It was bloody frightening, actually. Although I didn’t know what had happened, something was clearly wrong at the back end. I braked gently to a halt, got off and had a real scare when I saw it. I wrote to Suzuki GB more than once about this, and after several months they finally paid up for the replacement parts (the bike had only 6000 miles when it happened) and my train fare home on the day!
Tyre life has varied. The originals lasted a most satisfactory 17900 and 16000 miles front and rear, but because their maker was too shy to put his name on the sidewalls, I can’t tell you where to buy them. I then tried T61 Michelins which gave really good grip on the road and were OK on the rough, but were ridiculously short lived for such a light, low powered bike 8100 and 5400 miles front and rear.
I therefore changed to MT22 Pirellis. These seem just as grippy as the Michelins and the rear lasted 11300 miles, and was only replaced because I got a puncture and had to take it off anyway. The front has masses of tread left after 10000 miles - and I should hope so too.
SP400 chains have a short and unpleasant life. With a chain guard from the very minimalist school, a four stroke single's thudding power pulses, a 15 tooth gearbox sprocket, long travel suspension and a minimal cush drive in the rear wheel, I suppose I should be grateful for the 7000 miles I get out of them. I've tried buying a heavy duty chain but it makes next to no difference, so I now buy whatever’s cheapest. Odd that Suzuki should have specified only a 520 type chain in the face of such adversity.
The lights are lousy. The 45/40W headlamp emits a feeble glow, more to be seen than, to see by. The crappy relay lets the indicators blink once and then stay on, except when you rev up, whereupon they blink again. The rear lamp is OK, though, and, unlike some older Suzukis, the brake light is actuated by both brake levers.
As I mentioned earlier, maintenance is a doddle. Every 2000 miles I change the oil, clean the plug and filters, lube the cables, check the camchain and then generally look the bike over. Every year I change the fork oil and lube the clock cables. In all the time I’ve owned the thing I have never had to adjust the tappets or the carb, so I've left well alone.
If and when the tappets do go out of adjustment, it’s a simple screw and lock nut arrangement, although access could be simpler. I'll have to remove the tank, and to do that the seat must first. be unbolted. Fortunately, you don’t even need a feeler gauge to do the tappets adjust the screw until it is just seating, back it out one eighth of a turn, lock it up and there you go.
I had the second camchain, a split link job, threaded on at 31200 miles. This was the first time I had ever paid a service bill on the SP400. Taking up camchain slack has always been a fiddly job, as the plunger arm sometimes sticks. It’s best to take the whole assembly off to check, which only takes another five minutes. The ignition timing never moves because it’s CDI, although the earlier SP370 had points. Even working at my snail's pace a full service takes no more than a morning.
The vibes limit the bike’s long distance potential. Keeping the revs down to 5000 translates to 55-60mph in top, which is bearable for a couple of hours and also means that I can do 120 miles before the 1.9 gallon tank goes onto reserve. The most I've ever done on reserve is 19 miles, at which,point the tank accepted exactly 1.7 gallons. I'd travelled 141 miles on that, mind you.
However, I wouldn't want to do frequent long rides on it because of the upright riding position, the vibes and the hard seat. Going back to it after a few days on another bike, it does seem excessively vibratory. All the same, an acquaintance once toured France two up on an SP370, so it can be done. My longest day’s mileage was 280 miles - a trip to Donington Park and back from Maidenhead.
The spartan theme is continued with the lack of an electric starter. This has never bothered me as I have always enjoyed booting a bike into life. The decompressor lever below the clutch lever ensures that you can win bets on the SP starting first time. It always needs full choke in the morning; when hot, no choke but a little throttle. On all occasions, employ a long, swinging kick to kid onlookers that this is a real man’s machine.
Weak points are supposed to include the kick start, which can snap, and the oil feed to the top end. I've never had any trouble with either. I was able to check component condition when the camchain was replaced. The cam, cam lobes and bearing surfaces all looked really good, but there was a bit of wear on one rocker face. My faith in frequent oil changes was justified.
The drum brakes are adequate overall, although the fully floating rear one is cable operated and so feels a bit vague. Two up, things are pretty near the limit at times, but engine braking is strong due to the lack of a heavy flywheel. In fact, if used gently it can be ridden almost entirely on the throttle, which helps to explain why there is plenty of life left in the original brake shoes.
As it’s my everyday bike it doesn’t seem worth spending time cleaning and polishing as it's sure to be raining the next day. The appearance has therefore suffered over the years. The alloy rims and fork sliders have deteriorated, paint has come away from the engine and tank, and the indicators and exhaust downpipe have rusted. It gets a thorough wash and brush-up before the MOT test each year but other than that cleaning is, er, irregular. Good job I’m not proud.
You rarely see an SP400 advertised for sale these days, but as your editor says in the used section, they have loads of potential and are worth hunting down. I don’t know if he still does it, but Alf Hagon used to offer a 480cc kit which modified the stroke of the engine. A Hagon engine stuck in a Ducati chassis would make a really neat bike, but it’s just one of dozens of projects which I don’t suppose I will ever get around to.
Even rarer than the SP are the DR400 and GN400. The DR is a more serious enduro tool with a superior specification including full width brakes, a box section swinging arm, bigger engine bash plate, slightly higher compression ratio, different carb and a slightly bigger tank. It was finished either in white or that ghastly Suzuki yellow.
The buyer with a choice between a DR and an SP therefore has a bit of a problem. All things considered, the DR is probably the better bike even just for road use. However, bearing in mind that it was offered as an enduro machine, any used model has probably led a harder life than an SP of the same age. The GN400 was one of those awful factory customs from the early 1980s although it was fortunately mildly done.
The UMG claims the SP can be run to 35-40000 miles without problems. If mine is anything like typical, it can do so on a minimum of maintenance as well. Mine continues to plod along and I estimate that it will reach 40000, and so start living on borrowed time, around mid 1990. Looking back over six years, the bike has done everything I’ve asked of it and has never broken down, apart from that one near disaster. It's adaptable, providing you are not looking for high average speeds. It feels at its most pleasant when thudding down country lanes, and is also slim and brisk enough to make a good town bike. It will cope with motorway work surprisingly well but don’t expect it to be fun.
The SP400 has a lot of the charm but few of the vices of the big single. In conclusion, it’s a shame that there is no similar bike being made today. The Japanese seem unable to leave a good idea alone and their dual purpose stuff now looks too complex to me, with its water-cooling, multiple valves, disc brakes, peaky engines and electric starters. When the old crate finally wears out I will either have to buy one of these high tech ones, or a road bike like an MZ or something to get to work on.
Jeremy Irwin