Motorcycle recommission project - Suzuki GS750

LondonClassic

Retro Guru
I became the proud owner of this 1979 Suzuki GS750E recently.

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A mostly complete bike that turned over on the kickstart and had a tax disc present from 1996. The seller had bought a batch of bikes at auction to get to one specific bike and was offloading the other 5. In his brief time with the bike he'd had her running by hot wiring the igniton...for about 10 seconds until petrol streamed from the carbs onto the engine casing. The bike was very much billed as a project, which is a polite and glass half full way of saying its saveable with some work and money.

Heres a summary of the condition found:

Good
22K on clock
Aftermarket electronic ignition fitted
Laser 4-1 pipe
Tank had no rust inside
Koni shocks

Not so good
No history so no way of knowing if the 22K is genuine.
No ignition key
points cover missing and some minor chewing of the R side crankcase where somebody seems to have knocked it off
Brakes totally non functional.
4-1 pipe means no centrestand which will make no sense, practically
small oil leak where tachometer drive exits rocker cover
Stock airbox gone and replaced with pod filters
Wiring a bit of a rats nest and several bodges appear to be in place.

I could have adressed some of the intrinsic issues - like the brakes - and got her back on the road fairly sharpish. Cosmetically though the bikes needs a going over as she is now 45 years old and deserves some mid life love. So the decision was taken after getting the bike to run to go deep. The bike is getting a full strip and refurb (but not the motor if I can help it). Not to show level but to a usuable, safe state with some 70s patina.

I've owned some 'big' bikes but the only bike I ever full dissassembed was a Honda CG125 aeons ago. So this should be fun. I'll detail my progress here!

GS750 background (skip if you find tech bits boring).
The GS750 was Suzuki's first large capacity 4 stroke and was responsible for saving the company after the twin disasters of the RE5 rotary engined bike and stringent US emissions regs which sounded the death knell for their fun but entirely two stroke model line up in the 70s. Because it had to sell and save their bacon they took no chances. They were heavily inspired (copied) a lot of the bulletproof engineering in the Kawasaki Z1 but made the GS the best handling big bike of the 70s (a Z1 weak point). Isambard Kingdom Brunel would have been proud of the massive crank roller bearings and gear primary drive in the bottom end. Its so over engineered it can take around 450bhp in stock trim (accoridng to drag racers!). It only has to handle 72. This does make the motor heavy and expensive to make, however - but its reliability was legend. And they sold truckloads.

As well as making 550 and 1000 versions, this unit was the basis for all Suzuki four strokes going forward. The motor got 16 valves and became the GSX series from 1980. In 1985 they went to oil cooling and the GSXR series was born - and continues today.
 
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Current state: As of yesterday the bike looks like this:-
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Lots have bits have been removed including the carbs, exhaust, chain...anything connecting the engine to the frame. As I want to either powdercoat or DIY respray the frame that lump of a motor is coming out. Its a heavy bastard.

As I know very little about auto electrics I have been super cautous and labelled every connector, taken photos and started a diary of jobs with notes like 'blue circle 15 is battery negative to engine earth connector. Yes I am a dull man.

Inlet and exhaust has been blocked off to prevent corrosion while its stored in the shed.
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Electrics were never the Suzuki strongpoint. These work but I probably need to make a fresh wiring loom. The starter relay works right now...but needs replacing. I think the voltage regulator / rectifier may not be original and the fabled Honda superdream model which many owners switch to.
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I would suggest connecting the electrics back up and throwing in a fresh battery to check what works.

Likely something like a Boyer ignition on it, if it doesn't work straight away just get a new one.

Calipers are easy to sort. The brake pads have likely corroded into the calipers. Seals are cheap, pistons are likely £20 each unless you have a lathe and stainless bar to machine but if you do its easy enough to do.

Its been heavily messed with. Air box is gone in exchange for cheap pods so will likely never run right especially with the Ignition and Laser exhaust.
 
I would suggest connecting the electrics back up and throwing in a fresh battery to check what works.

I've had it running. All of the electrics appear to work - even the gear indicator! A front brake switch needs to be wired in at the lever/master cylinder and I have one. Not sure why they were considered options in the 70s.

I have no idea on the state of the brakes. They were either drained of fluid or leaked fluid :D. I expect the master cylinder seals to be shot..I may replace anyway for peace of mind. I bought a stock airbox in the summer and have the keyster carb kit to return everything to stock - you're absolutely right, no way I'm messing with pod filters and that laser pipe. A Delkevic stainless system is going to go on.
 
Front brake light switches weren't required till about August 1984 in the UK, the Suzuki sliding switch of the time was a piece of crap.
If the MC seals need doing it will likely have a rusted bore so just replace, new pattern MCs are cheap enough.
Even a Delkavic could cause problems but you aren't spoiled for choice.

Good news on the electrics at least.
 
Great project!
Can you get, make or get made a new wiring loom?
If you've got the old one out, it seems crazy to refit it - most breakdowns are electrical...

Some people love copying an old loom - I see you can buy the connectors - im sure motorcycle restorers will know of people, men i expect, who will do this for you!
 
Great project!
Can you get, make or get made a new wiring loom?
If you've got the old one out, it seems crazy to refit it - most breakdowns are electrical...

Some people love copying an old loom - I see you can buy the connectors - im sure motorcycle restorers will know of people, men i expect, who will do this for you!
Unless you've got access to 50 different colours of wire in various gauges it's normally cheaper to get one made than to make one yourself. 😉 a worthy idea though for sure as what's in there will be brittle and prone to breaking.

Normally an advance of 1 degree and different jets will get it running on the non stock exhaust well enough, glad you've got an air box for it, saves a lot of agro.

Frame powder coat used to be about a 100 notes plus blasting, I suspect it will be more now.


Gone are the days of cheap bits unfortunately, seems people.lole to bobber these things so parts have all but dried up.
 
Great project!
Can you get, make or get made a new wiring loom?
If you've got the old one out, it seems crazy to refit it - most breakdowns are electrical...

Some people love copying an old loom - I see you can buy the connectors - im sure motorcycle restorers will know of people, men i expect, who will do this for you!

Absolutely on a new loom. I don't want to re-use if I can help it and yes bad electrics (esp bad Suzuki electrics) will be the most likely the cause of on road snafus. The connectors and wires themselves are dirt cheap but the skills to copy what currently exisits I need to learn. I will probably go this way but I am tempted by the motogadget - in industrial quality digital controller for bike re-wires. Pricey though. One of the features is the ability to start the bike remotely from an android phone via bluetooth:LOL:.

Getting a loom made.....thats going to be even more than the motogadget. Rupert Paul (ex performance bikes ed) does custome re-wires but its like a grand to get a GS750 done. And I'd need to van the bike to him.
 
Unless you've got access to 50 different colours of wire in various gauges it's normally cheaper to get one made than to make one yourself. 😉 a worthy idea though for sure as what's in there will be brittle and prone to breaking.

Normally an advance of 1 degree and different jets will get it running on the non stock exhaust well enough, glad you've got an air box for it, saves a lot of agro.

Frame powder coat used to be about a 100 notes plus blasting, I suspect it will be more now.


Gone are the days of cheap bits unfortunately, seems people.lole to bobber these things so parts have all but dried up.

These folks do wiring supplies that won't break the bank. I have a decent crimp tool already. I am tempted to lay the current loom out on a board and try and copy it. That still leaves the OEM soldered wiring on things like the switchgear though. Need to think on it but all advice welcome - 100% on old wiring being a brittle liability.

I've been quoted £180 for a frame and swingarm powdercoat in black. I will really need to trust the coater as I've had a totally sh*t PC job on my Peugeot Triahtlon frame that was chip city. I vowed never to get a bike powdercoated again as its so hard to get off if it goes wrong.

I see lots of cafe racer type conversions yeah - most are horrible and they've hacksawed a perfectly good frame to get crappy results. Prices for some bits can be nuts.
 
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