Hacking: Suzuki SP370

It was just as well that the SP was light in mass, because one of its common faults was afflicting my bike - a stripped kick start gear meant I had to bump start the thing. I found second gear was a little more bearable, but even so, bumping a 369cc four stroke single is no fun.

I bought the bike after months of negotiation with a toe-rag who was a car mechanic and thought he should make a profit on the Suzi despite going trail riding on it for two years and 12000 miles. He wanted £375 and I was only willing to pay £200. He spent about £50 advertising it at his price and eventually lost heart and let me have it for £235.

I always wanted one and, in fact, almost bought a new one back in 1979 when they were heavily discounted to a mere £750. The only dealer I could find who had one for sale had used the front wheel in another bike and expected me to wait for two months for a new one to turn up, so I went and bought a used XT500 instead.

The bike had 23000 miles on the clock and the engine didn’t look like it had been touched, judging by the un-scarred appearance of the engine bolts and screws. As it had been used on green lanes the paintwork was tatty and various bits were bent, but nothing a bit of fettling couldn’t put right.

The clock now has 38000 miles on it and I’ve had the head off twice to fix valvegear problems — the other common SP affliction. Both the cams, bearings and exhaust valve all have a limited life because of poor lubrication and subsequent overheating. Luckily, the SP370 engine is a very simple and straightforward design no balance shafts, a mere two valves and an ease of disassembly that would make British bike owners envious.

The first time I took the head off found the exhaust valve slightly pitted but was able to grind it back into order. The second time, heralded by a sudden loss of power, was caused by the camshaft lobe wearing away - I was lucky, here, bought one by post from a breaker that was in perfect nick and cost £15.

The final problem with the SP is caused by the alternator burning out, which happens quite frequently if you use the bike on the road at night a lot and overload the puny generator. I rewind my own and have a spare ever ready. I’ve done four swaps so far!

I don’t take the bike off road, so have slowly been replacing the off road bits with road components. First to go was the hideous front mudguard mounted miles away from the front wheel. The lugs were already there and a plastic item found laying around in my garage fitted as if it was designed to. The front wheel with a useless SLS drum was swapped for a TLS drum from a Honda 250, which didn’t fit until I’d made some spacers but must have halved the braking distances.

A set of TT100s were fitted which stopped the bike from trying to flop over in corners. Shorter rear shocks were fitted and annoyingly, after all the hassle fitting the front -wheel, I then fitted CB250 front forks to even things out. This lost about three inches in seat height so that I could actually put my feet on the tarmac - huge ground clearance may be fine off road but it’s not needed on the tarmac. This all made the Suzi a great little bend swinger, although it would bounce around a little bit over very bumpy roads and weave above 75mph.

Top speed on a stock bike was 90mph, but this is easily improved by changing the gearing - you can take off in third gear on trail bike gearing so there’s plenty of room for altering the ratios. This also makes 70mph cruising much more pleasant as it used to be blitzed by vibes in top gear on stock gearing. I’ve been up to 95mph on the clock, but it wasn’t a very pleasant experience, what with thrumming primary vibes and a queasy weave that needed a yard and a half of road. Much more pleasant to limit speed to a licence endangering 80mph.

Fuel economy is one of the areas where the SP excels. It’s one of the few Jap singles, no, it‘s the only Jap single, that rivals those Ducati singles. I regularly average 80mpg and if] indulge in a spot of slow riding it’ll do better than 100mpg. The worst I’ve done is 71mpg. That’s the pay off for simple engine design.

In fact, the SP is the cheapest bike I’ve ever run. With long lasting drum brakes, a chain that never seems to wear (not so with long travel stock suspension, though), nil oil consumption between 1500 mile changes, rear tyres that last for more than 12000 miles and that exceptional fuel economy, I’ve never had it so good before.

Of course, the engine hasn’t been so reliable as it should, but I’ve been able to fix it myself. so no real problem. Indeed, that's one of the fun parts of my motorcycling, stripping down the engine and improving the cycle parts to get a better bike for minimum cost makes the machine feel more individual and like an old friend.

It doesn’t plod like an old English bike, you need at least 3000rpm up to make her go, but otherwise it has all the attributes and few of the problems of the British stuff. Just a pity Suzuki made the awful GN400 instead of a decent road bike.

Alfred Browning