CG125 Fast Idle Engine / Spark Plug Carbon Fouling

[Ingah]

Having got my CG125's engine going after not using it for ~18 months, having cleaned the carburettor and corrected a mistake i'd made: http://www.themotorbikeforum.co.uk/viewtopic.php?f=5&t=32372.

But immediately into another issue

Engine is running too fast, for want of a better term (doesn't sound like idle to me). Noteably when the choke lever is down (i.e. choke off), it runs faster and louder still. Even after i'd given it chance to warm up, and tried again.

I haven't messed with the idle at all ever since the mechanic set it up right a few months into my ownership (well over 2 years ago), so i suppose i could just try to turn it down, but due to the throttle cable needing attention first (see below) and my cautious nature, i don't want to mess with it - i'd prefer to fix what's gone wrong or changed than simply adjust the idle until it hides away what the real problem is (or worse, messes things up and i forget where it originally was set!)

Other important thing i noted is that there's no throttle free play - as well as the throttle twistgrip / mechanism not returning properly and consistently when released - so i'm going to buy a new throttle cable in case this is what's causing the issue. I see it as fairly probable.

This probably wouldn't even warrant a thread, if it weren't for the fact i took the (previously fresh) spark plug off the machine to have a look. It was badly carbon fouled, which wasn't bad considering i only had it running maybe 10-15 minutes (let it warm up to see if it calmed down when warm), and the engine hasn't been running since i last changed the spark plug (i.e. i put a fresh one in the bike for storage).

According to Haynes: "Carbon fouling - Dry, black sooty deposits leading to misfire and weak spark. Caused by an over-rich fuel/air mixture, faulty choke operation or blocked air filter".

I checked the air filter (despite being aware i'd serviced it not long before putting the bike away). It's clean and in good condition, bar the outer (very thin) material (a separate layer) having a slight hole in it. Nothing of concern to me.

[rennie]

Sounds like the choke is stuck on to me!

maybe not the actual lever/switch but the bit in the carb.

However small single cylinder 4 strokes do behave stranglely under choke!

Both Susie's and my Son's YBR 125s have to be left revving their nuts off

for ages before you can turn the choke off.

If you're absolutely sure that the carb is now free from all old fuel residue

I would suggest you look at both the throttle and choke operating cables

next. Make sure there are no kinks in them and give them a good soaking

in WD40 or something. Inside I mean just spray lots into top of cables

and leave overnight.

[eastanglianbiker]

remove the top of the carb and then twist throttle see if the slide is moving up and down as you hold top of the carb it might be that the cable has seized up and not allowing the slide right down into the carb when assembled

[Guest]

also check that the twistgrip isnt being fouled by bar ends and the like, effectly holding it open.

[Lumor_uk]

remove the top of the carb and then twist throttle see if the slide is moving up and down as you hold top of the carb it might be that the cable has seized up and not allowing the slide right down into the carb when assembled

 

this

If it is fully open you'll need to spin the cap round 180 degrees so it will allow it to slide right down.

it's the cylinder bit inside that is almost completely shut, make sure it is moving freely without any sticking

http://www.chinesemotorcyclepartsonline.co.uk/images/largeimages/CRB036.jpg