1980 Suzuki GS1000G: our bikes

Date 09.4.2015

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  • Motorcycle Trader

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1980 Suzuki GS1000G

This was one of the projects that took far longer than it should have, and I’ve really nobody to blame but myself. Thanks in part to the giant traffic jam in our shed – a collection of 17-ish bikes and a few cars will do that – Dr Gange the sidecar tends to sit neglected, all the way down the back.

Its state of tune has been deteriorating over time, which has supplied just one more reason to avoid the considerable task of digging it out for a run. Come to think of it, aside from the sodding Sunbeam, this has easily been my most troublesome bike over the years. That’s weird, as Suzuki GS1000Gs are notoriously reliable. Well, except when you attach a giant sidecar and expect the poor thing to haul what probably amounts to double its own weight.

DR GANGE’S CREDENTIALS

As with many outfits, this is basically a one-off build that started with an R&B chair. The front end was built by Bob Martin Engineering when Bob was still very much alive and well, as were the bike’s wheels, which are Suzuki hubs and spokes mated to car rims. Dennis Ackland, the founder of Megacycle, built the exhaust as a one-off many years ago. Then there was Dr Gange, a shed-dwelling genius who did the paint and an extensive refit, including all that slick chromed bar work you see.

Its list of custom gear goes on, such as the chassis mods by Premier Sidecars in the good old days, and then Harrop Engineering. The latter may be familiar from its V8 Supercar work – I suspect we caught them at a weak moment.

All that custom work takes time, but by far the biggest drama started when I decided to do something about a mild big-end knock. These engines are famous for running seemingly forever, despite the irritation, but I couldn’t leave it alone. The specialist crank rebuild was excellent, however the allegedly professional engine reassembly was a disaster. It required no less than three revisions (the final by Spannerman, after the workshop cocked it up) before the powerplant could be relied upon to keep its oil on the inside.

More recently, the throttle response was becoming erratic and couldn’t be relied upon.

A quick check of the state of the ignition revealed it was fine. The popular theory was worn membranes – plausible given the age of the bike and the fact those particular carburettors originally came off a very high-mileage motorcycle.

The plastic/rubber-like membranes in the top of typical CV carbs can be deceptive little buggers. They can look whole and still leak and, while it’s tempting to try, I’ve yet to hear of a successful long-term repair even if you do successfully locate a pin-hole. Replacement is the only viable option.

INSANE IN THE MEMBRANE

With many older bikes (this one is about to celebrate its 35th birthday), the big issue is finding the correct part from the original maker. When you do, cost can be prohibitive. I couldn’t find membranes for this model, but those for the very similar GS1100G are quoted at $616 for the set. Ouch!

By way of contrast, JBM Industries in the US, which specialises in carburettor diaphrams, quoted $US105 ($135) including shipping for its aftermarket alternative. The company has a decent reputation, contrasting with what is possibly the world’s most chaotic website. Anyway, I ordered the bits, which turned up within a couple of weeks, then they sat in the shed for close to a year.

A couple of tips for those who plan to follow this path: first, make sure you follow the instructions and carefully measure the outside diameter of the existing diaphrams. As JBM correctly points out, relying on the bike having the carburettors mentioned in the specifications is fraught with risk, as there are market-by-market variations. Secondly, ensure you let them know the brand of carburettor. If in doubt, include a quick photo of the part.

With the luxury of some holiday time to burn, installation turned out to be simple enough. In this case the mounting rings (there are two per carb) for the original membranes are dispensed with. Instead, the new parts rely on a thick centre section to locate them on the slide. Cutting off the old rings seemed all wrong, but it’s the correct procedure.

Reassembly is straightforward and I took the opportunity to gently clean any ‘varnish’ (dried out fuel) off the slides and bores to reduce the likelihood of sticking – particularly at idle. With this series GS (GS850/1000/1100G) the airbox can be a real bugger to refit – in time the inlet rubbers perish and shrink. I invested in new ones a few years ago, which was money well spent. This time, it was just a matter of leaving the airbox in the sun for a while to heat the rubbers and make them a little more flexible, then sliding it all back into place.

AND WE’RE BACK

With the best part of a year having passed since the last time it ran, Dr Gange was given a reasonably thorough check-over: battery (which is a large car unit in the boot of the sidecar, for easier starting and better weight distribution), oil levels, brakes, tyre pressures and fresh fuel. A quick prime,a few stabs on the starter and the old dear rumbled into life.

Ms M Snr, despite the fact she was sober, volunteered to come for a spin – so off we went. The result? Well, we’re not going to win any races, and I suspect another clean of the carby bores wouldn’t go astray as the idle ‘hangs’ a little high occasionally, but overall it’s a much happier piece of machinery. Throttle response is now consistent and the engine is doing pretty much everything a whole lot easier.

It was a great reward for $135 and an afternoon’s work and makes me wonder why in hell we didn’t tackle it a whole lot earlier.