CG125 running fast- help!!

[devilbelly]

hi everyone, i'm new to all this, first post.

Was hoping somebody could help me out.

I have just today bought a bike with a CG125 engine etc. Problem is that it is running way too fast on idle. I checked the air screw and to my surprise it was already screwed right out so you can imagine how fast it was going as I tried to screw it back in!!!

I checked the slide was returning fully on the carb and it is. There is a little brass screw at the bottom of the main body, I haven't touched it yet but, was hoping to find out what it is and whether this could have anything to do with the problem, if so how to sort it.

Any other suggestions would be most welcome too!

[jimpuntoy]

dont know what its like on urs but on mine the big screw on the side is the idle speed which you undo to slow and tighten to increase revs, throttle cable may be getting stuck? the mixture screw on mine is turned out 2 and a half turns from fully closed. the screw on the bottom of my carb is how you open up the float chamber thing and its also the big jet. how high is it revving at idle? is your choke fully off? dont know what else it could be.
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1992nsr125rk ..

[stinkwheel]

There are two screws on the carb. One sets the fuel: air mix at tickover, the other sets the idle speed. You would want to have the mixture screw set to factory level (usually 1&1/4 turns out, but this varies from bike to bike).

You would set the idle screw to obtain a steady tickover, first back off the cable adjuster on top of the carb so there is some slack in the throttle cable then gradually adjust the screw position (screwing out lowers idle speed) 1/4 turn at a time 'till you have it right. You may need to blip the throttle a couple of times to see where it settles. Then take up most, but not all, of the slack in the throttle cable.

Before all this, check the throttle cable isn't sticking or getting trapped somewhere. Might also be worth making sure the throttle valve is in the right way round (no offense, but 17 year old CG125 owners do some really dumb things sometimes).

It is also possible that there could be an air leak round the carb manifold. To check this, with the bike ticking over, spray the area between the carb and the engine with WD40. If the engine revs itself up, you have an air leak.

EDIT: Remember for next time, it is a good idea to check and note the position of the screws on your carb BEFORE you move them. Then if you make things worse, you can put them back to how they were.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.