There is not much better in this world than a lightweight motorcycle. Really the only thing better is a lightweight bike with a massive engine stuffed inside. And the only thing that trumps that is a lightweight bike with a light weight yet more powerful engine, which is exactly what this crazy Aprilia has.

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The RS250 from Aprilia is a renowned chassis, featuring suburb handling as well as being slim on the scale. Derived from the 250 GP bikes of old days, the RS250 is quite literally one of the best track bikes you can buy. That is if you can find one. Down in South Africa, Garth Evans was one of the folks lucky enough to find one, at least he was able to find the chassis of an RS250. With that Garth went on a tedious journey of creating his dream track bike, one that could rival the GP500 of his youth. Garth says, “I have always loved two strokes for the sheer fun of the ride—they might not be the fastest around a track compared to the new four strokes with all of the new electronics, but they make up for it in feel, fun, sound and smell.” With that firmly rooted in his psyche, Garth was set to start a 3-year journey to perfect his own RS250.

First came the engine transplant. Garth originally wanted something like a Yamaha RD500 or the famed Suzuki RG500 two-stroke. The issue of availability reared its ugly head, forcing Garth to go another direction. The engine of choice became the RZ350, a liquid cooled two-stroke built by Yamaha. While in stock trim the engine is less potent than that out of the RS, this engine is anything but stock. A well worked RZ will lay down some serious power, and it will do so with a surprisingly wide power band for a two-stroke. The parallel twin also comes as a much more compact package, making the process of shoehorning it into the RS frame that much easier.

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Garth didn’t just make a stock-for-stock engine swap, he completely rebuilt the RZ to a maddening level. He started with not one, but four RZ engines and some brand new Banshee cases. With some serious work, and a total of 40 hours spent re-working the cases to make everything fit. For internals Garth started with Athena cylinder liners with Wossner pistons, Hot Rods Stroker crank and of course all new bearings throughout. To get the power out of the mill Garth elected for new straight cut primary gears with a Hinson billet clutch. It’s okay if your drooling, it’s to be expected. To make everything fit Garth needed to fit an offset output sprocket, which came out looking like a work of art.

For fuel, the RZ is now equipped with Keihin PWK carbs and BMC pod filters and some V4 Force 4 reeds. To help burn that sweet octane is a fully adjustable ignition system; once burnt it all runs out a custom set of Jim Lomas pipes. I would break my own pinkie toe just to hear this thing run. To button everything up Mr Evans used an aircraft grade wiring harness, all in the name of lighter weight.

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Being a machinist and by trade with a background in Mechanical Engineering, Garth has the skill set that allows him to build some of the most incredible one off parts. That means this RS now features a slew of handmade billet aluminum parts, like the triple trees for instance. Why does he need different triple trees? I’m glad you asked.

Garth elected to live by the motto ‘go big or go home,’ by going the absolute biggest. This means the stock RS forks were ditched in favor of full race spec Öhlins from a Ducati Panigale while the rear shock was swapped for a Öhlins TTX rear shock. This obviously took some custom fabrication, something Garth is obviously no stranger to. With the best suspension setup money can buy Garth went even further, getting carbon BST wheels and Brembo brakes with 320mm rotors to finish off the handling goodies.

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To keep things tip toeing over the scale Garth built a custom lightweight subframe as well as an all carbon tail section and tank. With Renthal clipons and Tyga rear-sets, Garth was able to dial in the controls on this ‘YAMAPRILIA’ to fit him perfectly. An ST700 gauge sits just above the triple trees to let you know how everything is going, a nice simple touch to cap it all off.

Garth’s creation is not only unique, it’s also shaping up to be impressive on the track. While no numbers have been published we can only imagine that the new RS-Z350 is now much lighter than its original 360lb wet weight. It is also likely that the new power plant delivers a lot more oomph than the original unit, all while singing that gorgeous two-stroke sound. Now all it needs is a custom lightweight carbon fairing and it will easily be one of the coolest bikes we will see this year. Until then we will still be jealous of what Garth Evans has built.

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