Suzuki GN 125 - Revving uncontrollably

Dr Pepper

Hi,

Can anybody explain to me why my GN125 is revving up to 5-6000 rpm (by itself)? The idle revs screw is set quite low - about 1000-1500 when it's behaving itself. (And no, the choke is not left on all the time!). Once it's warmed up: Every time I pull up to lights and pull in the clutch or put it in neutral, the revs gradually climb up until it's roaring.. BTW, she's an oldie ('96) and been in the mechanics three times in the last few weeks (and now worse than ever).
Alternatively, is there a good motorbike repair/maintenance forum somewhere where this question would be better placed?

Thanks,
Brian

Haket

Any work been done on it recently ?. What did the bike shop say ?. Are the clutch and throttle linkages free moving and well lubricated ?.

seamus

I had a GZ125 that was doing this a lot. Just cleaned out the carb (there's a little screw that allows ice/petrol/dirt to drain out) and the problem was sorted.
Does it have a bad habit of cutting out constantly when it's cold?

Dr Pepper

Thanks guys,

The diaphragm in the carb was replaced a few weeks ago because it had a small tear in it (common problem with GN125's I hear) and it hasn't been right since. He's had it back twice since then and still the problems persist so I'd rather have a go myself at this stage. It's cutting out a bit before it gets warmed up.

Clutch and throttle cables seem to be moving freely (although I did have a problem with the throttle cable sticking a few years ago.. fine now).

I'll try cleaning out the carb. No idea how to do that myself but my Dad knows his way around a bike fairly well so I'll get him to have a look with me. Let you know how it goes...
In the meantime, if anyone has any more input, love to hear it. Thanks

echomadman

you might have a leak around the carb boot , get a spritzer bottle, like a window cleaner spray or a febreze bottle, fill it with water and spray it around the rubber grommit that the carb connects to the engine through, if the revs drop you have an air leak, take off the carb and apply some vaseline to the mating surfaces and refit it.

If that doesnt work you might need to adjust your pilot screw settings and/or check you dont have a stuck float in the carb

Hotblack Desiato

what echo said, but don't use vaseline on the carb boots, it'll rot the rubber. If it's very difficult to reassemble you can use a little bit of water or dilute washing up liquid.

Dr Pepper

Thanks. I'm gonna have a crack at it tomorrow so I'll give those things a try. Let you know

Brian

Dr Pepper

Gave it a try on Saturday. Took the carb apart completely and gave it a good cleaning. I think the problem was that the 'plunger' in the carb (not sure of the real name - has a needle on the end of it) wasn't moving smoothly up and down. Took it apart, cleaned it out, bit of WD40 and put it all back together. Also cleared out the little screw at the bottom where the petrol comes is. Not much improvement straight away although it seems to be getting better every day since! (Running much smoother and not so much revving)

Thanks again for all the tips,
Brian