CG125 failing to start - second opinion required!

[8v_Chris]

hi folks, couldn't see somewhere for new folk to say hello so i guess this will do here. Hello!

Ive read lots on this and despite some similar problems i cant find a solution. im more familiar with 80s vws and still learning in all things bike so please be gentle!

on to the problem. It stared a few days ago with a 2005 Honda CG125 that had been in storage over the winter. it was to be doing about 7 miles from my parents place to mine. took it out of the shed and it started without any issue and sat and idled to warm over about 10 minutes. did the usual stall if i touched the throttle until it warmed. as it rode on it began to feel like it was missing, especially on anything more than half throttle. over the next few miles it began to do it regardless of throttle position was doing its best to stall when riding. luckily any time it stalled it would come back to life more or less without effort but i really thought it was going to have me stuck at the side of the road.

so, thinking it was a carb problem i gave it a fill of super unleaded as i thought the higher octane would let it run on a little less fuel and i also added some fuel cleaner in too, not loads all the same, just enough. thinking id solved the problem i took it for another run and it just got worse. constantly missing and doing its best to stall and when it did stall it was a pig to get going again. wouldnt idle at all either. eventually got it home and it wont start at all, either with or without throttle, choke, anything. even putting fuel or spraying carb cleaner into the cylinder doesnt do anything either. it has electronic ignition so would just turn over and over until the battery died.

in order to try and fix it i assumed the carb was blocked so its been off, stripped down and cleaned with cleaner and reassembled with no difference. spent a right while being methodical and the jets are most certainly not blocked now if they were. there was no sign of anything in the bowl or any of the jets.

fuel is getting from the tank to the bowl so the carb had fuel. slackening the fuel screw lets fuel run out the bottom.

had the plug out and there is a good spark. gave the plug a clean but no difference. will be getting a new plug tomorrow to rule that out though. when the plug was removed it was sooty so its either rich or its a poor spark.

on the basis that im getting a spark im guessing the ignition coil is good and ive been told that if theres electronic ignition i neednt worry about the timing being out, especially as it was something that got progressively worse, it didnt just appear.

basically, what are peoples opinions on this? if the new spark plug doesnt fix the issue what should i be looking at next? is there something else in the carb that i should see or need to look at? Any and all help gratefully received!

[mauzo]

If it's running rich, have you checked the air filter?
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'04 CG125, '07 CBF500

[Commuter_Tim]

What does your air filter look like?
EDIT: What ^^^ he said, blocked filter, less air, richer mixture, black plug
EDIT 2: REMOVED INNACURATE ASSUMPTIONS.

Your carb does also have a fuel/air mix screw on the bottom of it, but this mostly just affects the idle mix and a small portion of initial throttle IIRC.
Also, does your carb have an accelerator pump on the side of it? (brass pipe with a rubber gaiter at the bottom of it)
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The above post is most likely nonsensical.

I ride a Bandit 600... badly.

[8v_Chris]

Thanks fellas. It's got a flat panel filter that reminds me of the k&n panel type sits on a car. It's Similar to this https://www.bike-parts-honda.com/thumbs/h/motog/13KCHRB1/IMGE/200_120/F__1500.png

There's also no brass pipe on the side. I had the whole filter etc off and tried to start it without one and it made no difference.

[8v_Chris]

had a little success. put a new plug into it and it went! it will go for maybe a second r two then dies so im assuming the carb just needs set up now. going to have a fiddle and adjust the idle speed to see. getting into unknown territory now.

[Snod Blatter]

Sticky choke mechanism? Float valve not sealing properly? Does fuel run nicely out the tap on the tank?
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1994 CB250, 1984 CBX250RS-E, 1989 K100RS, 1995 TRX850, 2016 Z250SL

[8v_Chris]

yes fuel flows through without hesitancy or anything. the choke seems good, doesnt appear to stick and the valve opens and closes as it should. as for the float valve, i dont know how to check that

[Snod Blatter]

Take the float bowl off, find a way to keep the carb vertical as it would be on the bike (hardest part of this), put a clean (or not if you enjoy the taste of petrol) bit of pipe on the barb where the fuel goes into the carb, and blow down it. Raise the floats until they push the needle valve into its hole enough to stop you being able to blow through the carb. The floats should be about parallel with the casting of the carb at this point (probably). If you can always blow through it, even a little, you need to clean it better or source a new valve.

If it's wildly out you can bend the little tang that pushes the valve upwards, only small adjustments are required. Bam, float level set, master mechanic you are
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1994 CB250, 1984 CBX250RS-E, 1989 K100RS, 1995 TRX850, 2016 Z250SL

[8v_Chris]

brilliant! thanks, ill get a go at that if i cant get it going. got it to run for about 30 seconds there by adjusting the mixture so maybe thats the issue but failing that ill check the seals.

[MCN]

super fuels probably wont be any good to your engine as it cannot burn it. They work better in engines with Knock Sensors. Most bike don't have them.

Make certain the HT lead from the coil to the plug is secure and in good condition. If it has any cracks or splits they bin it and fit a new one.
Most issues are ignition as the fuel system is pretty basic and robust on those bikes.

Battery connections clean and secure. Clean means remove the connections from the battery and give them a rub with steel wool (Brillo pad) very fine emery or wet and dry. The terminals are tinned so you will eventually clean off the tin and reach the copper if you get too busy with it.
You need all the power from the battery to supply the starter motor and the ignition. If there is any bad connection then it won't work so well.

Edit: Ditch the standard plug if fitted and fit an Iridium plug. (The Green Sparkplug Company were the cheapest source of plugs in UK.)
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[8v_Chris]

all sorted now! new plug seems to have done it then just adjusted the idle speed a little and thats her. just took it a quick 10 mile blast and its going the very best so thanks all or your help

[Commuter_Tim]

Just to mention, now you've got her running right, it can't hurt to measure and write down how many turns outward you have the idle screw and fuel/air mix set at.
So if you have mess with them again, you have a good starting point.
FECK ARSE!
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The above post is most likely nonsensical.

I ride a Bandit 600... badly.

[8v_Chris]