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Our bikes: 1978 Yamaha SR500
by Guy 'Guido' Allen, pics by Ben Galli Photography & GA, July 2021
Single Solution
After lots of effort and a few mis-steps, Guido’s SR500 is finally behaving itself
Picture this: photographer Ben Galli has arrived, expecting to shoot a front-end rebuild on one of my Kawasakis, but the tool gods are against us (hundreds of tools – everything but the one I actually need…) and there’s a forced change of plan. Let’s do a follow-up on the Yamaha SR500.
No problem. Haul it out of the shed. Evict the spiders and wipe off the worst of the dust. It’s been sitting for three months and, prior to some recent work, has a long and painful history of being a complete and utter bastard to start.
On with the fuel, find compression, use the valve-lifter to gently ease it over, then give it a boot. There’s an unpromising waffling noise. Okay, repeat the procedure and…womp! It’s started and happily settled into an idle after a few seconds on the choke. Unbelievable.
What’s more, it happily fires first kick for the rest of the afternoon.
That’s it, I’m selling it! Clearly our relationship has reached its zenith and we will never work together better than on this day. I want a photograph and a certificate, but let’s quit while we’re ahead.
Shall we go back to the start? I first tripped over this thing more than 20 years ago. Cousin Russell was on the blower from sunny Naracoorte in SA. He had spotted an ad for a bike in Melbourne and wanted me to check it out.
It seemed basically all there – the owner kicked it over without too much trouble and it ran okay. Clearly it had led an interesting life, as it sported a couple of attachment points for sidecar mounts and the owner mentioned something about a bigger piston. Not sure what size, but it makes sense that you’d be hunting additional grunt with a sidecar hanging off the side.
Russell duly bought the thing and had some fun with it, but it slowly and progressively becomes increasingly difficult to wake up. It became infamous on one trip, from Naracoorte to Phillip Island and back, at times requiring a tag-team effort with his mates to get it going. Mr R eventually buys himself a VTR1000 and the SR ends up being parked in a corner of the shed for over a decade.
Sadly, the bike outlives its owner and I end up collecting it from Naracoorte in South Australia, some time after his funeral.
A few years pass by before I finally work up the energy to tackle the thing (I got distracted by an SRX600 along the way) and life is not rosy in SR land. It will often start, but won’t run for any length of time. A couple of times it manages to fire up, get me just far enough from home to be really inconvenient, and then flame out and refuse to re-start. And they wonder why I drink.
Fortunately I have SR500 Club co-founder Paul Newbold as shed buddy for the revival exercise. His role is two-fold: to stop me throwing it over the back fence; And to apply his considerable experience with them to see if we can nut out the problem.
First target is the stock 34mm Mikuni pumper carb, which has a reputation for being cantankerous as it gets older. He does a clean-out and rebuild, but that doesn’t seem to wake the beast.
As a precaution, I also replace the ignition coil, plug lead and cap, along with the ignitor. None of this is terribly expensive and both the ignitor and coil are known problem areas. I figured this at least eliminated the ignition system as a possible cause.
Still no dice.
Replacing the carburetor is a popular mod on these things and the unit of choice for many is the round-slide Mikuni VM series in various sizes. In this case I rang the local distributor and had a long chat. In the end I opted for the more expensive flat-slide pumper in a 36mm bore. His view was this would provide the best overall performance.
Nice gadget, but we still had problems. In the end I tossed it to Dave at Dynobike in Moorabbin. He twigged there was an intermittent issue with it firing, even though the ignition system tested fine. What the hell?
Eventually some bright spark (Jack at City Auto Elec in Coburg North, if I recall right) recalled that these things had to have matching flywheel sets, or exactly this sort of problem occurred. Again, what the…?
How it ended up with a mismatched flywheel assembly is one of life’s mysteries. Presumably it’s a bitsa.
I get on the speaking trumpet to Newbold who says, “Hang on a sec,” as he retrieves a spare flywheel he was just about to toss for scrap. Finally some luck – it’s a match!
Dave wields some magic over it and it’s returned, along with a dyno chart showing a healthy 31.5hp at the back wheel, up about four from where we started before it was tuned, and about the same as they claimed new at the crankshaft. In other words, we have a healthy little monster on our hands.
That was with the stock airbox, and with an aftermarket exaust of unknown make.
More importantly, Dave improves the shape of the previous power curve, to the point where it's performing stronger and more consistently from a theoretical 65km/h through to 130. Nice work. (See the graph near the bottom of the story.)
Of course when I pick it up it decides to flame out when it’s luke-warm, which is poison on big singles. We get it going again, with a little effort, but my optimism is shaken.
It needn’t have been. On the occasions it’s been ridden since, it’s been a doddle get running and has been a joy.
Its modest power number is something near 180 less horsepower at the back wheel than Hannibal, my modded Hayabusa, but that’s okay. This is a very different bag of ferrets.
The steering is a little slow in stock form, but overall it’s a light and slim thing to thread through traffic. Braking could definitely be sharpened up, particularly at the front, and I suspect some alternative pad choices would go a long way towards fixing that.
Suspension response is fine for what it is. Fresh oil and seals up front have improved things but I need to put a new set of fork gaiters on, as the last ones perished in record time. Hopefully the fresh set (a different brand) will last longer.
Meanwhile, the rear is handled by a pair of Konis of unknown vintage, which do the job. Throw in some fresh rubber and you have something that’s a lot of fun for a gentle swing through a set of curves.
It's definitely showing its age, with the usual rust, oil stains and paint chips, but I'm not inclined to restore it. Instead, the aim is to halt any further deterioration. This is one of those machines that should probably be left as-is and enjoyed.
After all the dramas, it’s a good toy and it’s got a permanent slot in the shed. Like a lot of basic singles, it delivers more pleasure than the spec sheet or the sum of its parts would suggest. It’s a thoroughly enjoyable Sunday head-clearing ride. Cousin Russell would be pleased.
Join the Club
This club has been around for several decades and has always boasted strong numbers. It runs an annual rally and sends out the occasional newsletter.
It’s a great source of info and support for this series, including the 400s. See SR500club.org
Original SR500s
Several versions of the SR500 and its SR400 sibling have been produced over the years.
This series one was made for the 1978-79 model years and was the only SR500 sold through Yamaha Australia. The cast seven-spoke wheels with a disc brake at each end is the easy visual give-away.
A slow seller, it took a few years to clear the local stock.
Over time they have been hugely popular as a project bike platform, with a locally-built supercharged version being one of the wilder and more intriguing efforts.
Good
Simple
Delightfully easy to ride
Reasonable grunt
Not so good
Can be a bugger to start in the wrong circumstances
Not the quickest thing on the planet
SPECS:1978-79 YAMAHA SR500
ENGINE:
TYPE: Air-cooled, two-valves-per-cylinder, four-stroke single, dry sump
CAPACITY: 499cc
BORE & STROKE: 87 x 85mm
COMPRESSION RATIO: 9:1
FUEL SYSTEM: Mikuni VM34SS
TRANSMISSION:
TYPE: Five-speed, constant-mesh,
FINAL DRIVE: Chain
CHASSIS & RUNNING GEAR:
FRAME TYPE: Steel single-loop
FRONT SUSPENSION: 35mm telescopic fork, nil adjustment
REAR SUSPENSION: Dual shocks, preload adjustment
FRONT BRAKE: 200mm disc single-piston caliper
REAR BRAKE: Disc, single piston caliper
DIMENSIONS & CAPACITIES:
DRY/WET WEIGHT: 158/174kg
SEAT HEIGHT: 810mm
WHEELBASE: 1405mm
FUEL CAPACITY: 12lt
TYRES:
FRONT: 3.50 x 19
REAR: 4.00 x 18
PERFORMANCE:
POWER: 23.5kW (31.5hp) @ 6500rpm
TORQUE: 36Nm @ 5500rpm
OTHER STUFF:
PRICE WHEN NEW: Au$1900 plus ORC
See more about the bikes that have passed through our shed
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