cg125 carb - wisdom appreciated!

[DanF]

Hello all. I am new to the forum, and after browsing and learning, I am now here to contribute!

I recently bought a Honda cg125 2004 for the purposes of commuting to and from work and hopefully saving lots of money in the long run.

It is mostly fine however I think there is something amiss with starting/fueling/air intake. I have tried searching for the answer in old threads but I think the unique blend of eccentricities to be fairly rare.

I will try to be as concise as possible.

1) The bike will only start with the choke OFF/closed. Choke on and the bike just won't start. However as soon as the bike has started, it must be revved, or it just cuts out. Whilst holding the throttle open with my right hand, I must bend down and open the choke with my left hand! Only then will it idle. However does sometimes still cut out from here, and the occasional blip of the throttle is necessary whilst I get my gloves and helmet on and open the garden gate.

This seems very odd that it will only start with choke OFF, but only run with choke ON.

2) At no point does the bike run with the choke OFF. So I set off with the choke on, but even once the bike is warm, half an hour/ten miles away the choke is needed. When I have tried turning the choke OFF, the bike still cuts out.

Worse, if I do something stupid like stall, the bike will not start as the choke is ON. So I have to whilst sitting on the bike, and wearing thick gloves (in traffic) turn the choke OFF, restart the bike, then whilst holding the throttle open, turn the choke ON. Partly due to the location of the choke, that is very difficult.

Also running with the choke always open, the fuel economy is suffering.

3) Allied to this, upon removing the side panels, to my mind the air intake seems very poorly designed. The opening for the intake points inwards between the side panels of the bike, where there is little air flow. But the bike has been manufactured for over 40 years so this seems unlikely to be a problem?... but given that I am opening the throttle to get it running it seems possible.

Apologies for the long post, I hope you have stuck with it and are able to offer some advice, is something amiss here?

4) Also does anyone know of a way of modifying the choke handle so it is more easily accessible?

Many thanks, I look forward to reading your responses.

[mccluskeyd]

Hi there,
some thoughts on your CG go along the following lines....

Having to run with choke is usually two or three things, some more severe than others to your pocket & patience...

1) The way that CG's attach from the carb to the cylinder is a rubber laminated manifold. As people take them off and on they very often split and cause air leaks when the bike is running, and are quite hard to spot as you really need the negative pressure of the piston sucking air & fuel through the carb to give the correct conditions to get it to happen.
Spraying WD40 or carb cleaner over it while it is running sometimes gives an indication as to whether this liquid is taken into the cylinder or not as it upsets the running.

2) The manifold and the carb uses an "O" ring to seal the joints ; somethime they can be worn flat, or split.

3) Keihin "Pumper" carbs ; they are a truely horrible invention , fine when they left the factory, but once any home mechanic has a go at them and upsets them, they are a nightmare in my opinion. You can either opt for stripping down and making sure that no pathways /airways or jets are blocked and all jet sizes are correct, & no air leaks.
Or go for a more simple Keihin / mikuni unit ; there are plenty of new ones on e.bay made in China, or get a pre-Brazillian CG one and jet it to suit.
The last CG I had I used a 1970's Honda TL125 Keihin and it cured all of my running issues with only jetting to adjust once it was in place.

3) Worn barrel / ring / valve problems. In extreme cases if your engine is worn the only way some engines will run it to have the choke on, this allows a better seal between the rings and the surface of the barrel as it is more oily / less air in the fuel mix.
So the answer to that one is take it to someone with a comperssion tester and check it versus what it should be
: 1,324 kPa (13.5 kgf/cm2, 192 psi) at
450 min–1 (rpm) according to the Honda / Brazil manual that I have.
Haynes say :
"Cylinder compression pressure - throttle open, engine fully warmed up
CG125, CG125 K1, B 10.0 - 12.0 kg/cm2 (142 - 1 71 psi)
CG125-C, E 1 1.5 - 14.5 kg/cm2 (164 - 206 psi)".

Anyhow,

Hope that this gives you some pointers ; don't give up, CG's are great bikes, it's just you have to get past this problem....!

All the best,

David.

[ssray]

Sounds like the pilot screw is out of adjustment, the pilot screw controls fuel at startup and to just over tickover

The basics are you find the factory setting by screwing it all the way in(gently) then usually turn it anticlockwise from 1 to 2 turns out.

Ray

[DanF]

David and Ray thanks very much for your replies. I shall look into it this weekend.

I am new to motorbikes, and it does strike me that engines and fueling become a problem after a relatively short life in comparison to a car. My bike has only done 24,000 miles. A car with that mileage would still be expected to be running perfectly. I now the bikes rev high, but still... Also when I have read similar threads of people having problems, this problems develop with very little mileage.

Just a thought!

[_Iain_]

A 1.2 corsa develops 45bhp & revs to about 6,000. Under normal use it'll spin to about 2600 revs and the load is distributed over four cylinders. Most 125cc bikes will make 14bhp & rev to about 10,000 with all the load on one cylinder. It'll also get ragged up to the redline fairly often.

Proportionally, would a 450bhp 1.2 corsa engine last very long if spun up to 10,000 revs & thrashed flat out daily?

Just a thought!
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[DanF]

As I said, I know that they rev high and have extra stress placed on them, but it is a short life before problems develop.

[Robby]

It isn't just mileage to consider, also cack-handed maintenance, home "tuning", neglect, and being left standing for years are all things that kill bikes, and all likely on 125s. 20k is not high mileage for a bike engine that has been used regularly and properly maintained.

From your description, it sounds like the choke is behaving but you're confusing off and on. You need to have the lever one way to start, and another way to run.

If you aren't confused and the bike will only run with choke on, you have a problem. To solve the problem you need to get to the right starting point - no use in making adjustments to compensate for a fault when you can just fix the fault.

So:
1. When was the bike last serviced? Oil and filter, air filter, fuel filter if fitted, spark plug.
2. I don't usually recommend this, but it's easy on a CG. Remove carb, clean it. Get a can of carb cleaner with a nozzle and squirt it through any hole you can find.
3. Inspect the inlet rubber (carb to engine) for any holes, tears, or signs of ageing. Replace if suspect.
4. Set the carb to factory settings. Setting can be found in Haynes manual. Make sure there are no gaskets or O-rings missing - if it is a pumper carb then the tiny O-ring between float bowl and carb body is vital.

[_Iain_]

Regarding the mileage thing;

Paddys Varadero 125 is pushing 80,000miles & still runs like clockwork. Bikes like Honda's CB500 & Yamahas fazer 600 have been known to do over 150,000 in the hands of couriers, with ST1100 Pan's pushing over 250,000 miles.

On the other side of things, i've just had to replace the piston in my H100 at 8,300 miles because I thrashed the life out of it on cheap two stroke. I also lunched the bottom end on a GS500 aiming for a top speed run, and that had around 23,000 miles on it from memory - I replaced it with a 49,000 mile engine & I saw the fecking thing still running around maidstone a few months ago.

If you understand that they rev high & have extra stress placed on them why complain about the short lifespan? Surely you'd understand that the practicality & cost issues of the work required to spec an engine/chassis package to last that amount of time would most likely double or even triple the retail cost of said bike? Thus making it more cost effective for the consumer to simply replace the bike every few years. How on earth do you propose we sell this wonder 125 at £9,000 to the 17 year old who's just going to get shot of it in a year or two when he gets a car or a bigger bike? You struggle nowadays to persuade the kids to spend £2500 on a YBR125 rather than £1500 on a lexmoto commutery thing thats unlikely to last 10,000 miles. You just wouldnt be able to sell bike & the growing trend for chineese motorcycles is proof enough of this
____________________
Please be aware that the above post may be full of complete nonsense.
Riding: '07 KTM Duke II, Baotian BT49QT-20 Driving: '88 Volvo 340

[DanF]

Toby thank you for your reply. I shall be having a look at it today. Have a feeling the carb might be a bit shagged and some level of overhaul will be necessary.

Iain... I don't recall making a complaint. Rather an observation, which i was quite open about, But thank you for explanation.

Again I realise this is against the grain of motorbike enthusiasts. But reading the impartial reviews etc it seems the Chinese bikes are making great strides (as they have in cars) in a very short time. It stands to reason given their technology, engineering and financing available that they will continue to improve which is surely a good thing for consumers increasing competition and range.

[DanF]

I meant thank you Robby *!