Honda CG125 CARB problem.

[Arran]

Been having some problems with my cg125, i start the bike up and it is idling okay on choke, decent but high on half choke, and when the choke is taken off the bike rev's it's balls off like it's about to blow up( There is play on the throttle cable), it's that bad we have to turn it off to prevent any engine damage!! The carb's been cleaned, jets cleaned out, we have tried adjusting the accelerator cable and the pilot screw, nothing changes! i've cleaned the air filter out, replaced the gaskets! and still nothing, could it be that the carb' is just worn out, just can't figure out what's wrong with the bike!! Need to get this fixed asap or i'm just going to sell the spares off the bike and buy a new one as i've just passed my cbt and want to go for my mod 1&2 later this year! Any help would be great and also i can provide a video if needed. cheers.

[Tango]

Check the main jet needle......this has several slots on it and a c-clip to set the height......so just make sure the clip is in the correct slot......

Haynes manual would be a good help here......

[Tiggie]

sounds like a vacuum leak causing the bike to run far too lean. is the carb attached properly? any cracks on the mounts or the intake pipe?

[Arran]

Ello, just got some WD40 and checked the carb' was attached tight. We sprayed some WD40 around the intake manifold and kicked the bike up, it revved high, so i sprayed some more around the intake manifold to make sure i hadn't missed anything and the bike slowed it's rev's down slightly, it wasn't a massive difference but something we could notice easily by spraying the WD40, although the rev's went back up after...prob due to the WD40 dripping off etc..

Soo, could this been a air leak on the intake manifold? & We haven't played with the jet's Tango, but will take a look sometime this week. Thanks for replys too, just want this sorted asap.

[Tango]

Sounds like you've got an air leak around the inlet manifold somewhere like Tiggie has suggested.....make sure there's no splits in the manifold rubber and the carb is seated and clamped in there tightly.....

[Tiggie]

like Tiggie has suggested

 

wooo!!!!!! first time for everything

[Arran]

Well, to tell you the truth, the gasket was broke before hand, so i made one out of cardboard and soaked it in oil, we also put sealant around the gasket too, it's done up tightly, but where can i buy a new manifold from? ;/ I'm already looking now i just can't seem to find one! Also, that slight drop in rev's will declare an air leak? I'd have thought it would have to be more than that but you guys are better with this stuff than me anyway. cheers

[GazW]

Right, confused as anything here, what did you change when this problem started? Or did it just start?

What gasket are you on about? There's no gasket anywhere near the carb on a CG, the intake is directly jubilee clipped to the airbox (the fat side on the picture) and the side with the rubber o-ring meets the inlet manifold.. (Second picture) the manifold should be bolted straight onto the cylinder head.. I would put a lot of money on your homemade gasket being the problem seeing as how it has no place at any point between the airbox and the cylinder.

Where are you located? Someone local might be able to help, although I would at least buy a second hand carb from a breakers before selling the bike..

[GazW]

And http://bit.ly/ZT2ttW

[Arran]

Right, confused as anything here, what did you change when this problem started? Or did it just start?

What gasket are you on about? There's no gasket anywhere near the carb on a CG, the intake is directly jubilee clipped to the airbox (the fat side on the picture) and the side with the rubber o-ring meets the inlet manifold.. (Second picture) the manifold should be bolted straight onto the cylinder head.. I would put a lot of money on your homemade gasket being the problem seeing as how it has no place at any point between the airbox and the cylinder.

Where are you located? Someone local might be able to help, although I would at least buy a second hand carb from a breakers before selling the bike..

 

There is a gasket which fits onto the manifold on the second picture. And the problem came BEFORE i made the gasket! There air box has nothing to do with this problem, so just cross that out. I will be getting a next to new manifold and gasket from a friend who is breaking his cg125 so hopefully that will work, or at least enable me to change the air fuel mixture to what it should be. & My location is on my name tag to the left. Cheers.

[Voodoo]

I can't see it being the main jet needle if you haven't touched it.

This is a bit of a long shot but it happened to me once and that is just check the throttle assembly is located correctly. Not sure what the exact name of it is, but where the throttle cable attaches to the slider in the top of the carb. I once managed to fit mine incorrectly which was the equivalent of keeping the throttle fully open. I never realised what I'd done until I bump started it!

[eastanglianbiker]

i would check the slide in the carb the reason it is ticking over ok on choke is you are choking the engine once you turn the choke off the mixture is correct and revving like mad sounds like you have put the slide in wrong.if you look at the side of the slide that goes into the top of the carb it has a groove right down one side of it,inside the carb there is a locating pin the slide should be put into the carb so that pin and cutout line up allowing the slide to drop right into the carb correctly

[Arran]

i would check the slide in the carb the reason it is ticking over ok on choke is you are choking the engine once you turn the choke off the mixture is correct and revving like mad sounds like you have put the slide in wrong.if you look at the side of the slide that goes into the top of the carb it has a groove right down one side of it,inside the carb there is a locating pin the slide should be put into the carb so that pin and cutout line up allowing the slide to drop right into the carb correctly

 

We checked the slide and it all seems to be working, i think it must be an air leak in the manifold if there is nothing wrong with the slide! When the bike is on choke it runs almost fine, if the air is being cut off and it's using the air from the leak but with choke off it rev's high, which means it's getting air from the leak and the air box.

[eastanglianbiker]

check the colour of the spark plug electrode after allowing it to rev high with no choke as it could be far to rich or lean as you still havent said about the mixture screw setting

[Arran]

check the colour of the spark plug electrode after allowing it to rev high with no choke as it could be far to rich or lean as you still havent said about the mixture screw setting

 

After it rev's high, we check the spark plug and it's covered it petrol and we have to wipe it sometimes before it works again, there could also be something wrong with the spark cable because of this? And it's black too.

[eastanglianbiker]

if its black and wet then its getting far to much fuel and running rich are you sure you havent left out the main jet from inside the carb when you had it off to clean it?the main jet should be in the centre of the carb when you have the float bowl off also check the cut off valve on the incoming fuel side is working and set to correct height

[Arran]

if its black and wet then its getting far to much fuel and running rich are you sure you havent left out the main jet from inside the carb when you had it off to clean it?the main jet should be in the centre of the carb when you have the float bowl off also check the cut off valve on the incoming fuel side is working and set to correct height

 

The main jet is in there! I can't honestly remember if that description is if the bike is on choke or off...i'll take another look in a little while.

[Arran]

So just had a check of the bike and tried to get the inlet manifold off to my surprise there is another problem, and this is that one of the bolts holding it in place is so worn it cant be gripped by a spanner so cannot be removed. Any suggestions? I think i'm going to buy a new carb' and if that doesn't work then i'm going to have to go into my mod 1 and 2 test funds to have to buy a new bike

[eastanglianbiker]

can you not get a slightly smaller spanner and tap it onto the bolt/nut which ever it is.if it is a 10mm nut then try tapping a 9mm open ended spanner onto it of if you have old style spanners a 3/8 one but a stubbon nut/bolt is no reason to buy a new carb as you have still got to remove it to replace/repair the carb

[Tiggie]

try filing the sides down to give a better grip, or use some vice grips. do you have or know anyone with a dremel? lovely tool for reshaping or cutting off bolt heads and rusted nuts.

I have a set of bolt extractors which look a bit like a socket set which bite down into the bolt as you loosen it, not had a bolt stay stuck since!

[Arran]

I've got a new carb on the way now, i will try to remove the bolt, but will try the new carb first and see how that works. The carb wasn't expensive and can be used for another bike anyway if it doesn't make a difference.

[Arran]

New carb has been fitted and seems do have done the trick, the bike runs like a dream and kicks up first time every time. Had a problem with eletrics, has now been fixed although there is a problem with the horn wires which aren't working, as soon as that is fixed it can be MOT'ed then i can be on the road.

[Grumpy Old Git]

Don't throw your old carb - Strip; clean; re-assemble and test.

You should be able to spot what was (is) wrong and once sorted, you will have a spare 9or even an item for sale).

[klingelton]

if anything as well, you can practice stripping and reassembling the carb.

[Arran]

The problem was an air leak, we think. but anyway i prob will strip it and clean it.

Does anyone know how to fix the horn, it works, but the wiring doesn't... :S