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Old bike idle issues

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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I know this is a GS site but I thought some advice could be found here since many other sites offered nothing. Its worth a shot right.

History: 1982 Suzuki GN125 single cylinder 4stoke 10,000kms. Always garaged never ridden hard or never dumped. I am the second owner as of Jan 2005. Previous owner is a relative. Not 1 spec of rust on the entire bike. Not even any scuffs/scratches on the chrome or paint.

Found that the bike sat since 1996 with full tank of untreated gas with the pet valve ON. Right away I drained the tank (absolutely no rust) and carb. Pulled carb out of bike and completely dismantled carb of all removable parts. I scrubbed and cleaned as much as I possibly could without a good carb body dip. I reassembled shiney clean smooth sliding carb and installed on bike. New gas in tank and the bike started right away. I drained and changed the oil which also sat since 1996. Cleaned and oiled air filter. I restarted bike and allowed to warm up well.

Problems:

1) Fuel drips out of carb overflow tube when sitting not running....I have a new float needle/seat/oring on order as that was leaking.

2) The O-Ring between the engine and the rubber boot manifold thing was flat and hard. Is this oring/gasket supposed to be round like an oring or could this be related to my next question.

3) After warming up the idle is rough and sputtery. The return-to-idle is slow. Also the air screw does absolutely nothing to effect anything. I can tighten it up or loosen it any amount of turns. Only when the air screw is removed does the bike sputter out and die.

#3 is really confusing me but I am thinking it is a very lean problem due to the manifold oring/gasket thing.

Anyone with any advice on this should be simple single carb single cylinder would make me a very happy new bike owner.

I have been riding for a few weeks to see if things sort themselves out. Kinda interesting with bike wanting to die when clutch coasting or sitting at stops.
 
Hope I can help, my experience is with bikes of approximately 8 times the displacement!

The new float needle, seat and o-ring should help, but your petcock must be faulty as well. If the float rebuild goes well it should stop the leaking, but I would rebuild the petcock as well.

As far as the manifold o-ring, they should be round for the most part. All your symptoms are typical of a manifold air leak. I would replace it- even if it doesn't fix the problem, it's good insurance and you can rule that out as an issue.

You can test the manifold o-ring by spraying a fine mist of water at the manifold and seeing if the idle drops- or what I prefer using WD40 and seeing if the idle raises.
 
I have checked the petcock. It only has on/off/res. Think its a plain old gravity fed petcock however I may be wrong. It flows when on and stops completely when off. On the intake boot, I tried both wd40 and starter spray and no effect. However I tried greasing the gasket/oring a bit and it appeared to help a bit. The air screw still does nothing. Will install the new float parts and oring to see how things improve. I also will install a new float bowl gasket as the original was very hard and cracked a bit.

Thanks for the responce. :) Yes I get alot of chuckles over the displacement of this bike but hey it was a gift. And the fastest road I take around here to work is only 80km/hr for about 3 blocks.
 
Additional symptom:

The slow return-to-idle problem improves if I turn the idle screw down alot but then it wont idle without keeping throttle revin a bit.
 
THe o ring in the intake boot is around 2 US dollars. consider replacing it before anything else. Install a fuel filter on it, another 2 dollar part, to keep debris out of your carb, that may be the problem. Spray carb cleaner down through the fuel line and see if it improves.
 
Absolutely replace the manifold o-ring. Check the manifold too for any cracking or hardness. Apply some hi-temp bearing grease to the o-ring. Don't over-tighten and shorten the o-ring life. About 6 ft/lb is good, or per your manual. Make sure the manifold clamp isn't stretched.
You may still have some carb problems due to semi-blocked passages too. Especially if it takes a long time to warm up or starts hard when cold. That's a long time to sit with fuel in the carbs.
 
This is an awsome forum. I kinda answered my own questions by asking but the second opinions are valuable. Just for the heck of it I tried regular rad hose clamps in place of the manifold and airbox clamps and the thing purred great. Not a single stumble or studder. Had to turn the idle screw down. On the right track now.....just waiting for the replacement parts to arive now. Thanks alot guys for the extra input.

This winter (4 months from now) I will take the carb out and do a complete thourough (dip included) cleaning and possible rebuild. I can live with the air screw thing not working for now. Not expecting to get any better performance out of this massive displacement so I can make do till next year. Lol you should ride one of these...lol...wound right up in rpm in 5th to get a whopping 90km/h without any wind. Wife named it Piglet.
 
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