Ron Wood Hop-Up Kit
RON WOOD HOP-UP KIT
CW EVALUATION
Making the most of an MZ
WE'VE NEVER OFFICIALLY TESTED MZ’s Silver Star, the German company’s entry-level Thumper. Not that we’re unfamiliar with the likable retro-standard. Fact is, the bike has received thumbs-up for its classic styling, nimble handling and upright ergonomics. Too bad the same can’t be said for its air-cooled Rotax engine, which barely manages 28 horsepower and 13 foot-pounds of torque. While those numbers may be sufficient for 14-second quarter-mile runs and a top speed near 100 mph, it’s a far cry from the engine’s real performance potential.
For a fix, we contacted Ron Wood Enterprises (755 W. 17th St., Unit D, Costa Mesa, CA 92627; 714/6450393), whose 614cc Rotax-powered dirt-trackers and roadracers produce more than twice what a stock Silver Star can muster. Comparatively, Wood says, a healthy 500cc engine should make at least 45 horsepower.
Which brings us to Stage One. This consists of a 40mm Dell’Orto carburetor, throttle cable, free-flowing K&N air filter, more aggressive camshaft (#237-865), ignition timing advanced 4.5 degrees, 16-tooth countershaft sprocket and Wood’s slip-on megaphone and muffler. Modifications made, the engine produced a lively-and reliable, Wood alleges-42 horsepower at 8000 rpm, 14 ponies more than stock. Torque was up too, to 16 footpounds at 5500 rpm. Cost? $827. This doesn’t include labor, but most modifications can be made at home with a minimum of tools and mechanical knowledge. “It’s a simple engine,” Wood says. “I took one apart blindfolded once.”
Stage Two was more involved-and more expensive. First, Wood plucked the engine from the frame and split the cases. Then, he crammed a 97mm J&E piston into a new cast-iron liner, bumping displacement to 585cc. Larger, 36mm intake valves were next, followed by Rotax’s best race cam (#237-860) and a mild port job. Finally, to get the bike to idle on the street, Wood reverted back to stock timing. The payoff, measured at the rear wheel, is 54 horsepower at 7500 rpm and 21 foot-pounds of torque at 6500 rpm. Cost for Stage Two is $1015 over the initial $827, for a grand total of $1842. This, tacked to the bike’s $5500 suggested retail. While that may seem pricey, MZ’s U.S. importer, American Jawa, is reportedly discounting Silver Stars, making a Wood-fettled machine more affordable.
Because the Silver Star is a light bike (MZ claims 322 pounds dry), the newfound power-to-weight ratio is excellent. Acceleration is nothing short of impressive, with quarter-mile times plummeting into the mid-12s at more than 102 mph. And for us, that’s mission accomplished. Ö
