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????
needs a bigger main jet is my guess
has all the symptoms
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.
Quote from: Bixxer Bob on March 14, 2016, 11:15:42 PM
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 (http://www.ebay.co.uk/itm/HONDA-CG125-Chinese-125-pre-1998-carb-carburetor-carburettor-repair-kit-30B-/252297365310)
Float Height?
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.
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.
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.
Quote from: Bixxer Bob on March 15, 2016, 01:44:54 PM
I don't have any more free time before my op at the weekend so it'll have to wait.
Get well soon!
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.
here's the manual if you don't have it:
http://die-kleinkraftrad-ig.de/wissensdatenbank/reparaturanleitungcg125.pdf
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!
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.
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.
a slightly bigger main will cure what ails it :nod
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 :bug_eye
thats a mighty jump to get the fueling right from the factory .
Quote from: Bixxer Bob on March 17, 2016, 01:38:01 PM
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.
As the bike has been standing for a while and presumeably with the carb dry I'm wondering if the plastic hasn't shrunk / expanded as is plastic's want when exposed to fuels :^_^ Certainly parts for the CG are dirt cheap (see below) and it has to be worth a go. Putting in bigger main jets as Mustang suggested is certainly an option but would only complicate an already rocky road if the float height was off.
http://www.wemoto.com/bikes/honda/cg_125_br-f_j/85-91/
Complete carb repair kit - £15
New carb - £52
Ethanol degradation... always gets to the seals, and builds up a 'varnish. layer whilst in storage - unless you use an additive and/or drain the carb(s)
I do both now :nod
I know what you're saying, but I don't think they had Ethanol in fuel in the UK when this was put away.
It's gone anyway, her dad's problem now. Thanks again everyone.
Ok, it's back again for me to fit a rack and top box and I have it for a week while she's gone home to Lithuania to visit family. With some use aparrently it's running better but not perfect so today I had the carb off again. I found two things that I missed the first time:
Firstly, I checked the accelerator pump was working last time but neglected to identify the gallery that takes that spurt of neat fuel to the venturi. It was blocked, hence the feeling it was lean - because it was.
After blowing that through it still bogged before picking up when blipped and would even stop if I didn't back off the throttle to catch it and instead kept it wide open. This time though it felt decidedly rich so I messed around with pilot jet settings and accelerator pump adjustment for a bit but nothing made a great deal of difference so I whipped it off again (little bikes are so easy, less than 5 minutes to have it off and in bits). I checked the spec in the Haynes and this model (with Kehin carb) should have a 90 or 95 main jet. This one has a 110 so I'm going to order the smaller one and see what happens. It might be that somewhere along the line it's been into a shop to cure the bogging caused by the blocked gallery and they've upped the main in the hope that it might cure it, but only guessing.
That certainly fits with the evidence you're seeing :thumbsup
Bob,I'm wondering if you sorted that issue? My daughters xr125 has similar. She bought it 2yrs ago,but not used it. Now she wants to sell,and pay for repairs to her car(thats anotherstory..bloody VW's!!!) Anyway,I've checked the carb,and its clean. But it dies when you open the throttle,until it warms up,then its fine! Float height can't be adjusted,and I'm not sure what size main jet it has? Should I start there? Don't think this carb has accelerator pump as mentioned?
No, I've not completely sorted it yet although it's a lot better. I can only get at it occasionally as she's using it now.
So far I've blown all the orifices through twice with high pressure air fter soaking in carb cleaner. the tiny hole that bleeds air into the venturi at the intake end was blocked and clearing it made most of the difference.
I've also spent ages on the idle screw, the tickover screw and the accelerator pump so it now picks up cleanly unless you really blip it hard.
At the moment it's got a 110 main jet but should have a 95 or 100 so that's next. Although I think that will simply release a bit more top end power (I use the word laughingly) I don't think it's anything to do with the pick up. MY next plan is to increase the fuel injected by the accelerator pump and how early it does it because I think it dies beacause it's not getting enough fuel.
FINALLY!!!!!
It runs well. Manual says 95 main, it had a 110 so dropped it to 100. Pulled really well but plug was white so put the 110 back in, faffed around with the needle, it likes second down from top best. Mixture screw 1 3/4 turns works well, but the bogging if the throttle was blipped still remained.
Although everything looked ok, and after coming across the idea on a forum, I changed the very small O ring round the air bleed. It's not the idle jet, it's a tiny airway at the back of the float bowl. Anyway, it worked. And it now runs like a sewing machine. You can get it to bog very slightly if you give it very sharp blip so Imight have a bit more play with the mixture screw. But the O ring leaking seems to have been the issue.