162bhp ZRX? That’s a real man’s bike
CAST your mind back to 1981. Ronnie Reagan was running the world and Eddie Lawson was on his way to sealing the U.S. superbike title on a Kawasaki Z1000... but there’s one more name to remember and that’s Rob Muzzy.
Responding to an advert in American bike magazine Cycle World, Muzzy was signed as crew chief at Kawasaki, where he met Lawson and was confronted by a bike not a million miles away from the ZRX seen here.
In a world dominated by Ducati 996s and Honda’s new SP-1, the idea of riders winning titles on a lumbering Z1000 seems almost laughable. But back in the early ’80s the big Kawasaki was one of the bikes to own.
And once Muzzy had worked his magic there was no stopping it. Lawson scooped the ’81 U.S. title and went on to take the crown a second time the following year. The foundations for both men’s illustrious careers was laid.
Kawasaki first launched its ZRX1100 Lawson replica three years ago and now Muzzy – who is based in Bend, Oregon – has finally turned his attention to creating his own version. And since he’s the tuner who helped Lawson win his AMA titles in the first place, it’s not to be ignored.
And it’s fitting that Muzzy has come up with the bike now, just as his long relationship with Kawasaki’s racing effort seems to be coming to a close. They are bookends to an era.
Similarities between the old Z1000 and the ZRX end in the engine bay. Instead of the old bike’s eight-valve, air-cooled four, the ZRX sports a ZZ-R-derived 16-valve, liquid-cooled motor. Knowing he could go one better, Muzzy has taken it to 1136cc by increasing the stroke by 3mm and adding 1mm to the bore.
He’s retained the original steel cylinder liners and added his own forged pistons on custom-built conrods. Muzzy has also worked on the cylinder head and the end result has seen the compression ratio rise from 10.1:1 to a more sporty 12.9:1. Muzzy’s favourite X-1 cams and valve springs and 41mm Keihin carburettors, married to a Muzzy four-into-one stainless exhaust system, ensure the throttle response is instant.
Put everything together and you’re looking at 162bhp at the rear wheel on race fuel; a bit less on ordinary petrol, which the bike seems to tolerate without complaint. It makes the stock bike’s more than respectable 104.5bhp seem a bit pathetic.
The tuning work means you have to rev the bike harder to get the most from it – the power curve reaches its peak at 10,750rpm rather than the stocker’s 8500rpm. But when you’re rewarded by all those extra horses who cares? And a larger-than-stock rear sprocket helps with bottom-end acceleration.
We won’t complain about the flat-slide carbs’ restlessness at 5000rpm either, because by 6000 this bike is making 10bhp more than stock, and by 7000rpm it’s producing nearly 120bhp. From there, things become progressively more interesting.
Where the stocker retires after 8500rpm, Muzzy’s beast has crossed into 140-plus bhp territory and continues ravenously until 11,500rpm. By then, it’s still cranking out 150bhp and the sweetest four-cylinder music we’ve heard since... well suffice to say, it’s very sweet. But that’s not to say it’s outrageously loud; throttle back and you won’t attract too much unwanted attention from the law.
The engine work’s all well and good, but can that decrepit tubular steel frame take that kind of bhp abuse? Of course not. That’s part of its charm.
Or can it? According to Muzzy main man Doug Meyer, the dirt-bike style rotary steering damper below the bottom yoke is what makes it all possible. " Before we figured out the steering damper, it was unrideable, " he admitted. " You couldn’t hold the throttle open. The damper is really the key to the whole bike. "
That’s nice to know, but through one flip-flop corner on California’s tight and twisty Streets of Willow circuit, where you use the bike’s wide bars to nudge it from full right to full left while getting back on the gas, you don’t feel so confident.
There’s a slight rumbly, earthquakey warning of impending doom. Then, nothing. The old girl (who’s actually brand new) gathers up her skirts and rails on through. Whack the throttle open and you almost feel like you’re closing on Freddie Spencer’s Honda as the rear Dunlop scrabbles for grip and levers the front wheel into the air. Sure, things do feel a bit wobbly, compared to something like an R1, but it all adds to the fun.
But don’t get too cocky. Head down the Streets’ front straight and the Muzzy-tuned engine has enough grunt to propel the bike into turn one at speeds which its chassis was never intended to cope with. Entering the corner at 118mph would be fine on something like a ZX-9R, but not on the ZRX. Whaaa… ahhhh!… careful… butt-clench. Push the front, wiggle, slide the rear, wobble, ahhhh, swallow heart, clench sphincter. You only make that mistake once.
Get your braking done a little earlier and things are fine. You’ll find the ZRX is a slightly flexy yet always stable pussycat that feels deceptively light and controllable. That’s partly down to the steering damper and also modest suspension tweaks which include re-valved forks. The front end is stiffer than on the stock bike, making it more stable under braking.
Muzzy hasn’t touched the twin shocks and they work really well and damping adjustments actually produce the desired effects – even when controlling this much power.
That’s enough of riding around the track, what’s the Muzzy bike like where it’s going to spend most of its life... on the road? The answer is that it’s an absolute animal. You troll around in the doldrums of the powerband at minimum throttle whenever there are cops in the area, and you live for those brief snatches of road when you can thwack the flat-slides open and catapult yourself toward the horizon. And we do mean catapult.
We’re talking Hayabusa-level horsepower in a lighter, sit-up package with only that little bikini fairing to stop your head being ripped from your shoulders. This machine is better than any gym for developing your neck muscles – and a load more fun.
Although Muzzy has removed the balancer shaft – because it saps a tiny amount of power from the engine – the tuned ZRX doesn’t tingle any more than the stock bike. You could ride it all day provided your neck can cope and don’t mind stopping every 120 miles or so for fuel.
This is a machine which takes us back to our roots, when manly men like Lawson roamed the streets on their old Z1s and the rest. Ride it hard and you’ll end up with callouses on your right hand from holding the heavy-sprung Keihins open. But Muzzy didn’t build this bike to cater for the limp-wristed among us who would complain about such slight discomforts. This is a hot-rod Kawasaki, built by the man who’s become synonymous with the phrase.
Surely this won’t be the last Muzzy Kawasaki, but if it is, well, we can’t think of a more fitting end. Full circle. Thanks for the memories. Sniff...
The bike isn’t being imported to the UK, but you could order one or individual parts direct from Muzzy on: 001-541-385-0706.
Colours: Eddie Lawson replica green/white/blue
Engine: Liquid-cooled, 1136cc (77 x 61mm), 16v dohc four-stroke in-line four, 41mm Keihin carbs. 5 gears
Chassis: Steel double cradle
Front suspension: 43mm forks, adjustments for pre-load, compression and rebound damping
Rear suspension: Twin-shock, adjustments for pre-load, compression and rebound damping
Tyres: Dunlop D207GP; 120/70 x 17 front, 170/70 x 17 rear
Brakes: Tokico: 2 x 310mm front discs with 6-piston calipers, 250mm rear disc with 2-piston caliper
Weight, power to weight ratio
198kg (435lb), 0.82bhp/kg
Top speed (claimed): 155mph
Geometry (Rake/trail/wheelbase): 25°, 10.3cm, 145cm