Vintage Motocross Racing

John Stein buys a 1974 Yamaha MX125 and a 1971 Ossa Stiletto 250TT and goes vintage motocross racing.


| May/June 2014



Vintage Motocross Racing

John Stein (983) fights for position with former AMA star Scott Burnworth (8).

Photo by Bill Masho and Mark Holloway

Perhaps it’s some genetic deviancy, but the challenges of problem-solving and mechanical resurrection that old bikes offer are more than just fun — they’re irresistible.

So it’s little wonder I chose a pair of vintage 2-strokes, rather than nice new machinery, when I decided to pursue a national motocross title. The notion that it could be done cheaply was added incentive. But would it? Only trying would tell.

Affordable beginnings

You couldn’t start much lower than a 1974 Yamaha MX125, bought from a Craigslist ad for $700, for the American Historic Racing Motorcycle Association’s (AHRMA) Sportsman 125 class. However, one ride revealed the stock suspension was intended for flyweights doing laps in a dirt lot, as both ends bottomed at almost any provocation. Still thinking economy, I installed spacers to bump up the fork-spring preload and found a half-inch longer pair of shocks for $45 on eBay, and then tried it again at a local race. It was hardly any better. Luckily, a call to vintage motocross racer and Yamaha medicine man Dave Rymal located a perfect MX360 fork and triple clamps, a vast bolt-on improvement, for $200. I also installed a new piston and ring, points and condenser, Uni Filter, tires and chain for about $250.

Motor racing artist Hector Cademartori and I headed to Arizona Cycle Park for AHRMA’s first western national of the year — one of seven I had targeted. The little Yamaha was better, but it still bottomed on hard landings and the shocks and seat were punishing. The engine was also down on power in the 125 class and especially in the 50-plus age group class, which was populated by 250s and 400s. Still, the little bumblebee managed to win three of four motos and take both overall class wins for the day, trouncing much bigger CZs, Maicos and the like. Not bad for a total investment of less than $1,200. Maybe we had something here.

We left Arizona on a high note, inspired to develop the bike further. In the weeks before the AHRMA round at Sonoma Raceway, I yanked the front end and sent it to Race Tech for $515 worth of Gold Valve Cartridge Emulators, new springs, seals, fluid and labor. I also engaged Works Performance to build a $445 pair of steel-bodied Gasser shocks with dual-rate springs. The stock seat, with its tired 37-year-old foam, went to AMS Racing for a full rebuild, a purposeful inch taller to improve ergonomics, for another $175. SportCycle Pacific also welded on a $30 pair of footpeg extensions.

All of this improved rideability but not the problem of being outgunned to the first turn. So while the chassis was apart, Rymal also found a donor YZ125 engine for $100 and had it shipped to Scott Clough Racing. SCR rebuilt it with a new ProX connecting rod kit, a new piston, bearings, seals, cylinder porting, increased compression, a tougher clutch and a larger Banshee reed valve for $1,100. Since the YZ donor engine lacked an ignition system, Scott added a killer $528 PVL unit from Penton Racing Products — the go-to ignition for vintage bikes. The engine would now need race gas at $13 per gallon rather than pump gas, but at least it didn’t use more than 2 gallons per weekend.





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