...... In the good old days when big fourstroke engines plonked their way around the trials courses of the world 500cc units were king… okay so a few made their names on 350cc engines but in the main it was the big ones. Then the world saw the light thanks to riders using Villiers engines but even so this wasn’t considered a threat because a 500cc four-stroke was doing all the winning even as late as 1964. Then its rider, one SH Miller nipped out to Spain, popped back with a 250 Bultaco and carried on winning. The trials world started putting two and two together and ended up with 250. A few years later in 1972, one SH Miller turned out on a prototype Bultaco with a 325cc engine and the world went bigger again. Ultimately this increase in capacity caused other manufacturers to experiment in this area with Don Smith turning out on a 400cc Kawasaki at one point and Mick Andrews too having a near-400cc Yamaha in the Seventies. Bultaco produced a 370cc model for Martin Lampkin and other riders on the team and for them it ended with a 340cc model at the end of production. Not everyone could get on with the bigger engines and often while the styling and sidepanels proclaimed the top-of-therange biggie what was being ridden was slightly smaller.
It seems, according to a feature by Motorcycle’s man Peter Fraser in 1972, that while riding the 250 Sherpa to good effect Miller often wondered what the bike would be like with a larger capacity. Would it, he wondered, have the lusty low-speed torque his Ariel had? A check of the Bultaco barrel dimensions showed there was enough meat to bore it out to 83mm diameter – the 250 is 72mm – and this would add 75cc to the capacity. The 83mm piston originated in the flattrack racer sold in the USA. Riding the prototype for a feature in Motorcycle Fraser found all other components to be as the 250 version and with the bike on a weighbridge it was found to scale the same as the 250 or 203lb to be precise.
In his testing Fraser reckoned the 325 would happily pull a higher gear and in fact many owners did just that by increasing the size of the gearbox sprocket. Fraser also found the engine to be nigh-on unstallable and willing to accelerate from a whiff of throttle to launch up the test hill, the last few feet of which were vertical. He concluded his test with the statement, “…the 325 Sherpa is a sure-fire winner…”. He asked Miller if there were any downsides and the Irishman countered with: “yes, it’s £10 a year road tax as opposed to £5…”