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The bike was Don Smith's prototype production Greeves powered speedway machine.
Jansson tried the 165lb flyweight machine at its first ever outing at Hackney Wick stadium. His only criticism - slightly down on power at the start and coming out of corners, and the too-stiff front suspension.
But these two faults were easily corrected. Smith bolted on instant power by changing the 360cc cylinder and piston for Greeves new 390cc set-up, and tuning for methanol instead of petrol. Softer fork springs were fitted.
Now the ex-Greeves works trials rider is making further modifications and working on a second prototype which he and Jansson will ride.
If it is successful - and successful to Smith means beating the JAP and ESO-engined machines - he will go into production.
The first prototype frame was built in low-quality tubing so that any design weakness would quickly show up.
Despite this, it gave no trouble and the second machine will have an almost identical layout, but will be made from T45 or Reynolds 531 Tubing.
The frame is of bolted-up construction and individual tubes, most of which are straight, can be easily replaced.
With a conventional frame, a bent tube can mean a major repair job - possibly a disaster to a top rider who needs to keep his machine in service practically every night of the week. Wheelbase is 51.5 inches and seat height 28ins.
The 390cc engine is to be fitted with a 1.25 inch-choke Phillips fuel injector. Although it would be possible to open up the inlet tract another eighth of an inch, Smith believes that this, while adding to the top-end bhp of the engine, would rob power at lower revs.
Many proprietary parts are used in the first prototype, but the second will have Don's own countershaft, magnesium hubs and, possibly a diaphragm clutch.
To keep dirt out of the engine, a paper filter is fitted over a still air-box under the seat and a shield is used to protect the drive side crankshaft seal.
No price for production models had yet been fixed but Smith aimed to make it competitive with those of JAP and ESO. And he insists that he is not hoping to get a two-stroke speedway class under way, and added "I'm out to prove my stroker will beat the rest".
However, the Greeves project never really got off the ground. His motorcycle shop and the fact that he was dashing to and from Spain where he was helping develop a new Montesa trials machine meant that Don never completed developing the engine as he had wished.