There’s nothing that arouses curiosity quite like a rare vintage racing machine. Bonus points if it’s so obscure that you need to turn to specialist internet forums to pinpoint its origins — which is exactly what Cole Mahlowitz, the owner of this beautifully restored 1970s 50cc Grand Prix racer, had to do.
When Mahlowitz bought the bike, it was listed as a 1975 model “Czech” Minarelli 50 GP — a 50cc two-stroke racer with a six-speed box and a claimed output of 16 horsepower at 14,500 rpm. But when the bike arrived, he felt the need to dig deeper, because while the motor was undoubtedly a Minarelli unit, it also had “ČZ” stamped in several places.
Since the now-defunct Czech manufacturer ČZ never built a 50cc GP racer, Mahlowitz took to the internet to figure it out. Experts on European forums collectively believed the bike to be a pet project from an engineer who was originally part of Jawa’s racing department. And the “AMK Pisarky Brno” stickers gave away that it most likely raced at the Masaryk circuit in Pisarky, a suburb of Brno in the Czech Republic.
Mahlowitz is an R&D engineer at a firm that specializes in the 3D printing of metal components, giving him the unique opportunity to quickly prototype different functional and aesthetic parts. That meant he could geek out and get really technical on things.
The bike had been in storage for a few years before it was purchased by Italian collector Marco Gasparini, who specializes in 50cc race bikes from that era. When signore Gasparini got it, it was just a frame, three-quarters of an engine, and bodywork emblazoned with the colors of the Czech flag. He rebuilt it to working order and put it up for sale on his website, www.oldracer50cc.it, which is where Mahlowitz stumbled upon it.
A lifelong fan of two-strokes, with a particular fascination with the European 50cc GP racers of the ’60s and ’70s, Mahlowitz was a frequent visitor to the site. The Minarelli was just the donor he was looking for, so he snapped it up, and began the arduous task of shipping it from Italy to the greater Boston area — an eight-month process filled with red tape.
Once the bike was finally in his hands, Mahlowitz’s first task was figuring out exactly which direction to take the build in. Given the donor’s foggy past, he had no solid reference for a restoration job — so he scoured enthusiast websites like Elsberg Tuning for inspiration. From there, he took notes on everything from minutiae-like lever styles to what sort of styling cues were popular in Central Europe in the 1970s.
The Minarelli came as a basic runner. So it already had some beat-up bodywork, Marzocchi forks, and 18-inch Menani wheels with a Grimeca disc brake in the front and a ČZ drum brake at the rear. But there were a lot of gaps to fill in — and since this is a rare race vehicle, replacement parts aren’t exactly readily available.
Luckily, Mahlowitz is an R&D engineer at a firm that specializes in the 3D printing of metal components, giving him the unique opportunity to quickly prototype different functional and aesthetic parts. That meant he could geek out and get really technical on things.
One of those things was the drive nut that connects the crankshaft to the rotary valve; it’s a special long hexagonal nut, with a keyway that opens and closes the inlet port. By 3D printing and sintering several nuts with slight keyway variations, Mahlowitz could more accurately tune the engine. This same method was applied to a number of smaller parts — juxtaposed against parts that he opted to fabricate by hand in a bid to develop his metalworking skills.
One of the most difficult challenges was modifying the rotary valve housing to accommodate a 28-millimeter Dell’Orto carb, a setup more typical of 1970s GP bikes than the 22-millimeter unit the bike came with. Mahlowitz had to redesign the entire intake assembly while maintaining very tight tolerances — something that took countless hours of CAD work to pull off.
Somewhere in the process, he also upgraded the ignition from points to a CDI from a KTM 50 and installed a short-stroke crankshaft. The motor is still hooked up to the original six-speed, close-ratio transmission it was built with.
Not content with the non-period exhaust pipe on the bike, Mahlowitz decided to fabricate a custom unit with a properly tuned chamber and header. Designing, cutting, rolling, and welding together all the small conical cross-sections of steel — and getting them to fit neatly inside the fairing and underneath the frame — was incredibly tedious. And because this was his first legitimate welding job, he went through three iterations before he created something he was happy with.
For the bodywork, Mahlowitz roped in Eric Silverio at Krazy Kustoms. Silverio had his work cut out for him — he had to patch and repair the fiberglass, then reinforce it to make it more robust. He then resprayed the frame and fairing using the exact paint scheme that the bike had arrived in. Why? Because when Gasparini sold the bike, he made Mahlowitz promise not to change the livery.
Finishing touches included a few period-correct decals, including replicas of the original AMK Pisarky Brno stickers on the fairing. The Minarelli also sports neat details like a new hand-made switch panel on the left side and a Motoplat tach that runs from 4,000 to 16,000 rpm.
A year after he started the project, Mahlowitz finally fired it up … and quickly realized what a handful the temperamental race machine’s extremely narrow power band made it. But he was happy anyway because he’d finally ticked a major item off his list: own a vintage Grand Prix motorcycle that represents the ultimate in small-capacity, two-stroke performance.
The fact that it looks totally period-correct — but at the same time sort of hard to place — makes it all the more special.