Carb question

[Bixxer Bob]

Right, bike in question is a 1998 Honda CG125 with 3600 miles on the clock.  It's in good nick having been stored for many years, and even has the original tyres, which are about to be replaced.  I've given it a full service (about an hour - there's not a lot to it to be fair) but my problem is with the carb.

It needs full choke from cold, will fire first kick then stop. It won't restart on full and needs only half choke.  It then starts and ticks over but any throttle causes it to stall.  It re-starts readily enough and once it starts to warm the choke can be released and it will then rev.  IT runs cleanly throughout the rev range once warm, but will cut out if the throttle is blipped.  If the throttle is opened carefully the revs pick up normally.  It will blip quite happily if the revs haven't died back to tickover.  The carb has an accelerator pump whihc is supposed to stop this happening, and is adjusted IAW the manual.  Adjusting it either way from base setting doesn't improve it and tends to make it worse.  I've stripped and cleaned the carb, all jets and galleries are clear.  The accelerator pump gives a small squirt of fuel when actuated so I presume it's ok. I've tried adjusting the pilot jet and again, it's helped a bit but even on best setting, it still does it.

Ideas????

[Mustang]

needs a bigger main jet is my guess
has all the symptoms

[nickjtc]

Are you absolutely sure all of the orifices and air or fuel pathways inside are clear? Did you stick a guitar string or whatever into every hole? If the bike was running ok before it was parked it is unlikely to need a change of jet/s, imho.

[JoeDirt]

Ideas????

I would buy a carb-kit and rebuild it. You discount weak springs, bad seals, and leaky floats.

http://www.ebay.co.uk/itm/HONDA-CG125-Chinese-125-pre-1998-carb-carburetor-carburettor-repair-kit-30B-/252297365310

[Timbox2]

Float Height?

[Bixxer Bob]

Lots to think about there.  Because it runs so well in all other respects, and having done so few miles I'm doubtful about seals etc.  Everything was in remarkably good condition inside and even though it has spent so long standing in a shed, there was only a grain or two of sediment in the bowl.  Yes, I poked the galleries and blew them through. 

What I didn't say earlier is it only has one previous owner ie it's been in the same family from new and they've never had it apart so everything, such as the jet, is original. 


On reading a bit more about these bikes last night it seems they were set up to run lean and be frugal hence the incorporation of the accelerator pump (not seen one of those since my old Volvo....) which injects a gob of fuel if you move the throttle quickly so I'm going to have a look at that again as I think that's where the problem lies.

Thanks for your input though, not being carb-minded I thought I might have missed something.

[Sin_Tiger]

I did an XR (basically the same engine) a couple of years back with similar symptoms and decided it was the pump as well. Just all cleaned up and soaked the seals in some linseed oil to soften them, they appeared to be natural rubber rather than nitrile. Was not perfect but got better (or just got used to it) By London it was as good as it got until it reached Ulan Batar.

[Bixxer Bob]

Thanks Niall,  I think I'm just going to get the owner to run it for a few days and see if it improves. I don't have any more free time before my op at the weekend so it'll have to wait.

[nickjtc]

I don't have any more free time before my op at the weekend so it'll have to wait.

Get well soon!

[BruKen]

If you blip the throttles and it dies with a gasp it's lean. If you blip the throttles and it drowns with a stutter and gurgle or wants to stall then picks up and revs like the clappers it's rich.  Going by your description I'd say lean and the choke is the giveaway and before I did anything else would check the float height.
I certainly wouldn't be recommending it is ridden around to see if it get's better if it's lean.

[BruKen]

here's the manual if you don't have it:

http://die-kleinkraftrad-ig.de/wissensdatenbank/reparaturanleitungcg125.pdf

[Bixxer Bob]

A blip of the throttle results in it cutting out, not dying or stuttering or anything else.  No momentary increase in revs just a bit of induction noise and it stops.  But it revs cleanly if the throttle is opened normally, not blipped. 

The Haynes states that the post '85 engine / carb with the accelerator pump set-up is designed to run lean for improved emmisions hence the need for the pump.

Thanks for the link!

[BruKen]

It's definitely too lean then. I know on the wifes CG125 when she was learning that it was a bit of a devil when cold. You had to ride her on half choke until the engine was good and warm. But other than that it was a cracking little motor and very reliable and forgiving. Again, look at float heights.

[Bixxer Bob]

Float height is non-adjustable, the plastic floats and lever that closes the needle valve are moulded as one and have to be replaced if there is any wear.

As I can't do anything to it in the next couple of weeks the owner is taking it back today and her dad is going to have a look at it.

[Mustang]

a slightly bigger main will cure what ails it 
honda likes em lean

my dirt bike that was offroad competition use only was so lean it went from a 135 main to a 172 to sort it out 
thats a mighty jump to get the fueling right from the factory .