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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.

big boyeeQ: Hi guys. I’ve just written this message late at night because I’m really getting annoyed and, asking for help.

I’ve just bought a used Big Boy pit bike (125cc), that didn’t run when I bought it. I’ve replaced the spark plug, installed a new air-filter and changed the engine oil. The plug does have a ‘spark’ when I kick over the engine, so it’s not that. I’ve also taken off the carb and cleaned it to perfection as the jets were blocked with old, and sticky, petrol.

But it still won’t start and the engine seems to have good compression. Have you any ideas what I could look for next?


A: Yes we can advise and it’s an easy thing to check. Take off the two small valve covers on top of the engine and check the tappets for free play. They’re easy to adjust and you only need a 9mm spanner and pliers to hold the top of tappet.

You’ll need to find ‘feeler-gauges’ as well and set the clearance to 0.15mm between the tappet and the top of the valve stem. Once set turn the engine over a full cycle and check again.

This is a common fault if those bikes don’t start. So that should take away your anxiety.