tech help header 750

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gs850 2Q: I’ve just been given an old (1980 I think), Suzuki GS 850 – the one with the hefty shaft-drive. It’s been standing for a long time, so after a good clean I tired to get the engine running with some degree of success.

However, the biggest problem was the old exhaust, which isn’t the original system. I’m not sure what it is, but it’s black with a rotten silencer. I managed to fit a silencer to it (4-1 system) and now the bike looks better, at least.

I had to take off the carbs to clean them and they have ‘pod like’ filters on them, again I’ve replaced them with new ones because they were trashed. I noticed the main jets are 105s, which I believe to be the standard size.

So my question is – seeing as the bike has a 4-into1 system, and ‘pod’ filters, what jet size would you recommend seeing as you seem to be quite good with classic bike questions? It would be great to get them right the first time so I don’t have to take off the carbs and stuff around them again. Looking forward to your response.

Chris Cummins.

A: Yes Chris we’ve spent many hours ‘fiddling’ around with these types of jet settings. We’re not sure if you’re at sea level, or Jo’burg altitude though?

We’d recommend starting off with 125s, as they seem to be a good base setting for these types of modifications. If you’re living at altitude you could try 122.5s, or maybe a 120 main jet. It might be difficult to find them though so you might have to search around local ‘old’ dealers and the like.

Hope this helps with your new/old bike…

Replied: April 23rd, 2024

Suzuki GS 850

Q: My uncle has given me an old Suzuki GS850, the one with the shaft drive. I managed to get it running and went out for a ride, but suddenly the bike came to an abrupt stop and I could smell something ‘odd’ coming from behind the air box.

When I removed the side panel I realized it was coming from the battery, one of those yellow one’s, and when I took it out it was swollen and cracked down one side.

So I was wondering if you’d have any ideas on what could cause this, because I’ve never seen anything like it before?


Piet Stock.

A: There have always been issues with early big Suzuki’s and the charging systems. I’d predict there’s a short inside the stator behind the left side engine cover. Over time the copper windings become brittle and especially the three wires coming from it to the voltage regulator/rectifier units, which control the correct voltage and current.

See if you can get/borrow a battery and check the voltage with a meter onto the battery terminals, and make sure it isn’t more than 13.6 volts +/- above 3,000rpm. But if the readings are ‘strange’ you’ll have to replace the stator I’m afraid, which can be very expensive, but you can install it at home with very little tools. Maybe replace the regulator/rectifier as well for a new complete charging system to be sure?

This is what we’d recommend, replacing the whole system, and a new battery of course.

MT 09Good day Billy…

Q: Perhaps you can help? I have a Yamaha MT-09, nice to ride but every time I ride around town, between the 1500 to 3000rpm range, the bike tends to ‘surge’.

The sound from the exhaust doesn’t change but there’s a noticeable change in speed, as if something is grabbing and releasing. I’ve had the throttle bodies synchronized, but still with no change. I’m now thinking of mapping the ECU – any advice?

Phillippus Opperman.

A: Before you go up that expensive path there is one thing you can check that riders tend to forget. Buy a decent fuel-injector cleaner and put it in to the petrol tank, these can sometimes remove deposits from the injectors that could cause your irritating problem.

Does the bike still have, or did, the ‘power-valve’ installed. If set incorrectly that could also have this affect?

Try these recommendations first and let us know if it makes a difference?

gearsQ: Hi guys and thanks for a superb site, we go onto it everyday, so keep it going.

I’d just like to ask a question. I read about ‘straight cut’ gears and/or ‘helical cut’ gears and was wondering if you could clarify the difference, and the advantages, if any?

It was just something that popped up in our local pub conversations – looking forward to the answer.

A: Both are usualy used in the primary drive from the crankshaft to the clutch/gearbox. Quite simply the helical gear system is to make the mechanical engine noise, not so noisy, and that’s about it. However if you put a lot of extra power though a helical drive (turbo charging for example), it can ‘deflect’ the gears between the crank and clutch, as they can push/ride apart, causing irreparable damage.

Straight cut gears do make more mechanical noise but offer a stronger direct connection between the crank, clutch and gearbox – drag racers especially choose this due to the shock loading off the line. If fact all modern super bikes have primary straight cut gears now because of the high horsepower output.

If you look into a car gearbox they’re usually helical cut – again to keep the mechanical noise to minimum.