Honda CG won't start revving

[jabulmer12]

Hello gurus, I am in need of some help with my little CG. Its a Brazilian -ST so the newer shape but with out the electric start, its running the older brazil engine with a points setup now after the old engine blew up. This morning I went to start it and it just continually revved and spat a few flames out of the exhaust. I have toned down the mixture screw and now there's no flames but it still continually revs, I also adjust the idle and disconnected the throttle with no change. Interestingly when the chokes on it still runs where as before due to a design flaw it would normally stall, any ideas?
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Mots: 12/10/11 - Pass!
Current Vehicles: Honda CG 125

[Aff]

Is there an air leak somewhere?
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Current Bikes:Honda 929RR Fireblade, Honda CD200 Benly (Project), Stomp Z2 140
Electric Bike Project

[ricklincs45]

Have you done some work/had some work done on the bike recently? It's very unusual for this to happen 'overnight' so to speak.

Adjusting the mixture screw will make no difference to over-revving, so set that back to its original position.

Regarding the choke, the bike is meant to stall when it has been started and is then warming up - you shouldn't be trying to run her for more than around 20 seconds with choke full on; usually around 10 seconds is the maximum you should need before knocking her onto half choke.

As previous poster has mentioned, this problem sounds like a (huge) air leak. You have checked that the throttle slide is going up (and more importantly) fully down when the twistgrip is operated? If the throttle is fully down when the twistgrip is closed, any air leak is likely to be from the cylinder head back i.e. between the air filter and the inlet manifold stub.

Rick
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Author '80 Bikes, and counting...' Currently getting frustrated with an MZ 125 TS.

[unitynotsocri...]

as other posters but just check you've not snagged a choke/throttle cable.
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nearly a normal tax paying tosser.......with ferrileness suzi100,cg125,cb125scb100n,cb175,cd100,cj250t,kh250,c15,125 bantam,super 6,rickman gs750,xt500,250rs,dt175,lifan125,dolomite1850,metro,Morris220ld,morrisfg,leyland princess,range rover,corsa,vw camper .now struggling with legs. MORE ORDER = MORE CHAOS

[Rogerborg]

Fess up, what were you doing to it last night?

Disconnected the throttle at what end?

Is there some resistance / spring in the throttle cable?

Air leak in the inlet rubber, or the spring that pushes the slide down has snapped, or the throttle slide is sticking above the idle speed screw.

If it's like the Mikuni carb on my copy-bike then the throttle slide has a wedge shaped ramp on it that needs to be aligned with the idle screw. I'm picturing you opening the throttle wide, lifting the slide up clear of the screw, it rotating slightly in the barrel, and then dropping down so that it's being held right on top of the idle screw.
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[mudcow007]

i took my carb off t'other week to clean the bowl

ressembled everything after 6 or so kicks the biek sprung into life running at full pelt

i had put the throttle slide in the wrong way around so the slide was stuck at the top

[Rogerborg]

Yup, that's what I suspect, but surely op would have told us if he'd had the carb apart...
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike