You learn something new everyday. Two days before getting astride our new correspondent’s Yamaha RX-Z I was immersed in Stealing Speed, Mat Oxley’s must-read book on how 2-stroke tech crossed the Iron Curtain. Did you know that expansion chambers had their roots in the Nazi V2 rocket programme?
And that the Japanese only mastered the stink-wheels after Suzuki got the East German rider Ernst Degner to defect, taking with him all of Walter Kaaden’s secrets developed for the MV factory bikes? Read the book, you will love it if you’re a bike nut.
And then ride a 2-stroke, with an expansion chamber. You’ll love it even more. Nothing, nothing, nothing and then… braaaaaapppppp… loud, smelly, rabid acceleration as it screeches into the power band. Truth be told it isn’t much quicker than our modern 4-strokes but the sensory overload feels like a million miles an hour, all of it on scarily skinny tyres as 2-strokes were incredibly sensitive to weight.
Incredibly sensitive to the mechanic’s fingers and ears too. Everything had to come together. An expansion chamber without the correct porting was pointless. Both without CDI ignition was silly. Without the right jetting you’d be starting at a seizure. And after all this you had to try new a sprocket too, maybe even a flat-slide carb, and then start all over again.
Tuning 2-strokes, it’s a dying if not dead art. Back in the day when the mosquito fogging machines were raced I remember mechanics carrying boxes of needles and jets to fine tune the fuelling, no laptop and reams of data.
Head of the plug chop? Accelerate hard through the gears and then kill the engine and coast into the pits where the mechanics could divine from the condition of the spark plug whether it was rich, lean or spot-on.
Riders had to have a sharp ear for that death-note micro-seconds before the motor seized, two fingers always on the clutch though most often too late to save them from a painful outcome. Motors were stripped and rebuilt before every session. Two-strokes had a very narrow band for everything and even with tuned road bikes you had to be careful not to run it too lean lest you hole the piston.
When it all ran perfectly though, wow. You can get 30bhp from a properly tuned Yamaha RX-Z and when you open it up, it feels like twice as much. The Yamaha RX-Z frame is super-light and agile, and the Z’s bodywork gives it a retro-cool race-vibe that was quite difficult to match.
An aftermarket front disc makes a world of difference to how much longer you can keep it pinned. The noise from the wailing exhaust, parts traffic like Moses did the Red Sea. It takes you back to your carefree youth, until it starts to splutter and everything you read about 2-strokes seizing comes back to haunt you.
Check out our other ‘Gone,but not forgotten’ blogs here.