MATCHLESS G80
Last month, Derek Pickard introduced us to the delights of the 1980s British-built Eurobike. This time he considers the available upgrades and evaluates the modifications made to his own café racer
Last month, Derek Pickard introduced us to the delights of the 1980s British-built Eurobike. This time he considers the available upgrades and evaluates the modifications made to his own café racer
Some trad classic fans became instant critics of the Devon-built Euro/Brit bike when it was first introduced. They were quick to point out how the last of what they described as the ‘real’ Matchless G80CS bikes had produced the same quoted power output two decades earlier, and it was easier to start. Such claims aside, there are a number of tweaks which raise the performance of the Rotax-engined Harris Matchless.
Firstly the stock exhaust is restrictive and makes the motor sound too much like a whimper. You can either replace the muffler in total or cut off the rear part (where it gets restrictive) and weld on a freer flowing end section.
Secondly, Rotax make a series of cam options and the one fitted to the stock G80 is the mildest. Going from the touring to the sports type may drop a bit of torque around 2500rpm but a fair lump of extra power above 4000 is gained. And for such a modification the original, big Dell’Orto carb is the right size.
Going back to making the standard set-up work better, we’re left with the problems of the stock carburation with the aggressive pumper facility on a large carb. The fact is that a 36mm pumper carb fitted to a 34mm inlet is nothing less than stupid. Interestingly not all manufacturers who used the same spec 500 Rotax engine agreed with Matchless on the choice of carburettor. Whereas Harris wanted to boast good performance and fitted the 36mm pumper type Dell’Orto, MZ used a 35mm Bing CV carb, Jawa a 34mm Amal Concentric Mk2, Armstrong a 32mm Concentric Mk1 and Harley (yes they made a Rotax-engined army bike) a 30mm Amal Concentric Mk2. And most of those bikes enjoyed a reputation for being easier to kickstart than the G80. Amazingly, all claimed about the same maximum power output of 33 to 34bhp and most used the same cam.
The conclusion is bloomin’ obvious, in that the 36mm Dell’Orto with its accelerator pump is too big for the road cam. To improve things, the choice would be to either fit something like a 34mm Mikuni off a Yamaha XT500 or, if a rider prefers to stay within a 2000 to 5000 rev range, a 32mm Keihin carb from an
XL500 would be right on the numbers. I went the way of a VM32 Mikuni, which makes the engine super sweet. For the record, the allimportant numbers are 27.5 pilot 1.3 turns, 2.5 slide, 6DH3 needle centre notch, P-2 159 needle jet and 185 main. (It should be noted that the factory’s USA-model used a Mikuni carb, fitted an emissions statement placard and had wider handlebars.)
Remember the golden rule: a slightly smaller carb may lose a small amount of top end power but is most unlikely to show any drop in mid-range torque. Traditionalists need not get too upset about the use of Japanese bits as Rotax already used the Nippon Denso generator, ignition trigger and coil.
The last obvious conversion which improves things is to lower the overall gearing. The makers’ choice of a 20 or 21 tooth gearbox sprocket is too optimistic for the light-flywheeled engine and it exacerbates the rough running at low revs. A swap to a maximum of 19 teeth for the gearbox sprocket helps heaps. The lack of traditional, 500-style flywheel effect from this engine may be fine for a dirt bike, but most riders find it bad for normal road use. A popular improvement is to bolt on the extra weight disc to the generator rotor the way the army spec bikes have.
Another small but vital piece of work is to screw grease nipples into either end of the swinging arm pivot shaft which has been drilled and threaded. Regular greasing prolongs bush life. Apart from those mods, nothing else needs doing. This bike really is that good.
My G80 now has a number of upgrades and conversions which make it run better and look more British. They include a classic-era BSA silencer, Mikuni VM32 carb, classic-type alloy rims, Norton 8” 2ls front brake, flat bars with conventional classic controls and a caféstyle hump back seat.
TAKEN FOR A RIDE
So what is my own, upgraded G80 like to ride? The biggest real difference is the ease of starting. The slightly smaller VM type Mikuni carb with the cable choke means the motor can be started predictably when hot, cold and in-between. Bloody wonderful. On the move, the classic-style BSA muffler really makes even this foreign engine sound just right. A gentle bumping sound at tickover rises to a welcome barking crackle when the throttle is opened, right up to the unmistakable raspy rip of a single at full noise. Love it.
Performance is improved from stock only by fitting a smaller gearbox sprocket to lower the gearing. This helps make up for the lack of flywheel effect at low revs as it raises the revs to the road speed and makes everything that bit faster while being noticeably smoother. Sure it runs out of numbers below the red line that bit quicker when playing flat out stuff out in the country but in reality that is not such a problem 99% of the time.
When I start pushing the top speed fun, the limits of the Commando front brake which I fitted become clear. Going to a good, 1960s style sports drum brake from the competent late-80s Bonneville disc with Brembo hydraulics is a good reminder of why sports bikes had to make the shift away from the charismatic looking twin-leaders. Even after detailed setting up with oversize linkage pins, good linings and spot-on adjustment, this drum is only just acceptable for a 500 middleweight. It not only lacks the power of a disc but the stopping power is not linear with the handlebar effort.
What this means is that after years of being spoiled by good disc power, the operation of a 2ls brake is hard to accept. A small effort gives very little stopping power, a bit more sees the twin leading shoes come thumping in as their self-servo layout bites, and squeezing that bit again results in not much more braking power. The feel is weird and wrong. OK, the Commando sports drum looks good but where it really matters – on the road at speed – even a relatively good drum set-up comes nowhere near a good disc brake. It’s tempting to refit the Bonnie Brembo layout again.
While I’m complaining, the other grumble is at the seat. Although the new G50-style saddle is no more than foam and vinyl added to a replacement Bonneville seat, it definitely becomes flat and uncomfortable after an hour or two. This is a definite case of R&D by the Triumph factory where their 1980s Bonnevilles with more foam (height and width) may have looked a little too touristy but they certainly were better to sit on for longer rides. Like the brake, my modification is a visual improvement but it’s not as practical in actual use.
The other part of the riding position, the new handlebar layout, is fine. The Norton straight handlebars feel as good as they look. The conventional British chrome levers have sufficient size to exert good leverage on the clutch and front drum, and the normal twistgrip has the right angular action for the slightly smaller new carb.
One excellent aspect of the G80 which cannot be overstated is the really good handling. The combination of moderate mass and this bike’s layout – wheelbase, steering geometry and suspension set-up – makes for superb behaviour in the bends. Harris got this one dead right.
All-in-all, a tastefully modified G80 Rotax makes a good road classic. It looks good, starts well, makes all the right noises and has more than enough overall performance in the vital areas of go, stop and turn. Better still, this classic has a very modern engine which while still being a 500 single is utterly bullet-proof. Rev it, scream it, take it past the redline, hold it wide open to howl out of the corners, and do all of those as much as you like. The Rotax doesn’t vibrate, leak or break. Definitely the finishing vital touch to making a 500 British single that does everything right.