The legend of the Yamagamma!
As trick and ‘new’ as the Gamma was in 1983, some parts of the RG250 in its early guise at least, left something to be desired: mainly that motor…
Suzuki’s common 54mm x 54mm bore and stroke that the RG500 racers used was used, so it was hoped the motor would be a marvel – and it was, to some extent, but it only pumped out around 45bhp and the chassis could handle so much more. Some experts claim that it took until the Mk.3 with the Suzuki powervalve ‘AEC’ (Automatic Exhaust Control) (50bhp) for the bike to get the engine it truly deserved, but by then (1986-1987) the Suzuki RGV250K Gamma was already waiting to be launched: too little, too late.
Before then – and with some RG motors popping here and there – what about a substitute motor? Yamaha’s ubiquitous RD350LC Powervalve had the answer. Compared to the RG, the YPVS chassis was a little more previous generation, but clever people saw that the engine mounts on the
RG250 engine were in exactly the same place as on an RD250LC/350LC and in turn the same as the YPVS engine mounts. The YPVS motor also chucked out a healthy 55-60bhp. The only modification required was to make a new rear engine mount up and some said that it was former CMM contributor and legend Stan Stephens who did the first ‘Yamagamma’ or sometimes it was called a ‘Gammaha!’. In a previous CMM Stan said: “I bought one of the very first Mk.1 Gammas from Suzuki and built the Yamagamma straight away a long time before anyone else. In fact, I don’t think anyone else built one until I did the Performance Bikes article of the time – although I may be wrong! I did the PB article so that people could build their own and stop them ringing me up asking how to do it! My tuned bike running 38mm Mikunis and our own expansion chambers did 144mph with an 11.2 second standing quarter in the rain at MIRA.”
To make the conversion, you’d need a YPVS engine, loom, CDI, reg/rec, coil, YPVS servo, switch gears and carbs. Once the engine was bolted in, your next headache would be the air-box and it was found that individual filters worked best. Care had to be taken as to where the YPVS servo was located (right-hand side). Early bikes were soon joined by later Mk.3 and 4 versions before the RGV negated the need for YPVS speed.
That said, today these hybrids are still well respected and the sweet-handling RG250 Mk.1 or 2 with a 31K motor is a joy to behold.