Adventure Bike Rider Forum

Need some help chaps, my girlfriend is getting her sons CB125F ready to sell (as he's at Uni and needs a car now) but it has a tickover issue, it runs fine when cold but dies once warm, its been like this for a while apparently.
In the summer I gave it a service and checked the valves, oil change, new plug etc which made no difference and trying to adjust the throttle stop on the throttle body made it either tick over at 2500 revs and "hang" when you blip the throttle or it dies, no way of it being anywhere in between with the most minute of turns on the stop. It has only done about 50 miles since then.
It was Mot'd last week by the local bike shop I use and they had a look over it while it was in, checked, the timing, checked the valve clearances, checked the injector spray pattern, checked the compression and all ok, they suggested either throttle body or fuel pump which I can buy 2nd hand but won't know if the new parts are ok or faulty, the mechanic I use for trials bits suggested resetting the throttle position sensor but I can't find any info online on how to do this.
Anyone got any advice on how to move forward without spending a fortune on this as its being sold as soon as its fixed.
Cheers

Greetings,

An interesting conundrum and a bike that I am not familiar with in its present form.

The most common fault and perhaps cheapest check seems to be the exhaust valve clearance which appears critical for this engine.
Looking on the internet two possible faults which seem like the cheaper parts routes to try first are the oil temperature sensor and loose electrical connections. The lambda sensor or even throttle body are also highlighted as potentials but these would be more expensive to replace just on suspicion. One unusual one was a faulty clutch switch!

Perhaps this link might be of some help or at least interest to you; http://www.honda-cb125.com/misc.html

Maybe somebody who has experienced the same fault might be along soon with the definitive answer. Please let us know what you do to cure the problem.

TTFN

Hugh.

Didn't early TE Husqvarna's suffer with this problem? Engine oil or coolant temperature sensor fault from memory which meant it was 'on choke' when trying to start from hot.

My carb'd Husky certainly suffered from starting problems...because Luigi had put the wrong jets in the carb at the factory after getting pissed at lunchtime.

Richard Simpson Mark II wrote: ↑Wed Dec 16, 2020 10:22 am My carb'd Husky certainly suffered from starting problems...because Luigi had put the wrong jets in the carb at the factory after getting pissed at lunchtime.

My experience was from a mates fuel injection bike which wouldn't restart after a petrol stop on the IoM.

You may find this article useful as the issue is discussed
https://bikesandtravels.com/biker.aspx?ride=7294

First things first, drain all the fuel and put fresh in it. I doubt that's the problem but eliminate it as it's easy.
Next check that you're not building a vacuum in the tank by opening the filler.
Next disconnect any temperature sensors and see if it runs cold and warm and if there's any change in symptoms.
Then start looking at spending money on changing stuff.

Just to add more guesswork intro the mix, I had a cbf125 and one of the main issues was fuel pump problems. They run so lean and hence their fantastic mpg, that it can be a fuelling issue with the pump.
Second hand pumps are quite cheap and might be worth changing.
Good luck

Again, a different bike with similar sounding problem (although not the starting bit as that was fine, just could not get it to idle properly). Turned out to be my error. When putting the carb back on I had inadvertently rotated it a full 360 degrees tensioning the inner part of the throttle cable. Faffed around for ages before I figured out what had happened.

Thanks guys - some answers for you to ponder
Fuel - its been like this for 2 years so new fuel isn't going to make any change I think, vacuum in tank - i'll try that one - only sensor on it is a lambda as far as I can tell, tried disconnecting it and made no difference

CBF125 - this is a different bike and had issues with the fuel pump (think there was a recall) the bike I'm dealing with is a CB125F (also known as a GLR 125 - apparently where your F is changes a lot )

Valves - been checked by me then re-checked by bike garage and all ok

Another suggestion was to check for air leaks into the engine so I'll check that then order a throttle body as I can't find any info about the TPS or even find where it is - its not listed on the parts list
https://www.fowlersparts.co.uk/main/img ... 9dfa.png?6