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Home Repair And Restoration

CBF125 (Almost) No Start

Discovery Date 9 September 2022

By Ren Withnell

This poor clapped out 125.

The engine cover over the alternator and starter motor
I suppose it's looking a little tired these days.

It's not at it's best anymore. It burns oil faster than a 2 stroke, it clatters and rattles and now I suspect some of the sensors and electronic controls are not operating within prescribed tolerances. 

It still starts fine but the tickover needs a little assistance until it's warm. It will then tickover fine but you have to ease it down to tickover to be sure. Much like an old 2 stroke it needs the throttle blipping during gear changes or after a long overrun. It feels like nursing an old tired out of tune carburettor machine. 

While I'm a highly skilled operator of old knackered things (insert your own rude, saucy or inappropriate thoughts here) even one as deft of touch as I can occasionally cause the worn out oily slack piston to cough and stall. This, well this has become a problem. When it does occasionally splutter to a halt it's not always keen to restart. 

"Kft kft kft kft... Kft kft kft kft". Hmmm. "Kft kft kft kft kft kft kft kft ". It has eventually always got going and carried on as though there never was a problem and there never will be another problem again. It just seems to take 10 minutes to eventually sort itself out.

"It's flooded you moron!" I hear you scream. Yes, you're right. So I remove the easily accessible spark plug, check it over and let the barrel breath a while. "Kft kft kft kft kft kft..." Probably flooded again innit. It's oiled the plug? No, in fact considering how worn the engine is the plug looks really good. "Kft kft kft kft kft kft kft kft kft..." The spark looks good. "Kft kft kft kft kft kft kft kft kft..." 

Eventually it kft kft kft's then starts to catch Kft kft dum kft kft dum dum kft dum kft dum dum dum dum dum dum dum dum Brum! Hop on the bike and continue as if it was all in my stupid imagination.

Tell you what though. The battery is ancient, I'm pretty sure it's the original and yet it can crank this little and admittedly low compression 125 for 10 minutes of frustration! I mean how is that even possible? I suppose the regular use and just damn good luck on getting a good battery to begin with helps?

It died again on Friday. 

While messing and checking the plug I was getting frustrated. With it back together I tried to bump it but without a push or a hill I was getting nowhere. Bump it while cranking? I remove the clutch switch wires to permit this.

Interesting. Very interesting. I crank the motor via the starter when in gear. I really really ought to expect the bike to jump forward as the starter turns the engine that is in gear and the clutch is out. I mean with such a great battery I am considering using the starter to help me push it home if needs be. When in gear and pressing the starter button I get "Kft kft kft kft kft kft kft kft...".

Aaaaaaah. Yes. Aha! Obviously. It all makes sense now. Of course. Right. I see. I get it. The starter clutch sprags are worn out. When it's cold they're engaging but when it's warm they are not. 

Exploded diagram showing the starter clutch and associated parts
Item 2 is the starter sprag clutch, and likely worn out by now.

The "kft kft kft kft kft" noise sounds like it's trying to start but at best the motor is turning slowly, at worst it's not turning at all. The kft dum kft dum kft dum is the cooling starter sprags starting to grip the flywheel. Eventually it will start when the oil cools enough and the engine spins fast enough. I did wonder why it felt like it had no compression. I did wonder how the battery could crank for so very long. It all makes sense now.

Should I fix it? Naaaaah. There's only another 2,750 miles to go to the 100,000 miles mark. I'll be able to sell it on as a brand new bike then. 

Advertise here and maybe Ren would buy a new starter clutch?

Reader's Comments

Ross said :-
Nearly there, you could almost push it to 100k from there! When you reach that milestone are you gonna put the poor thing out of its misery or just keep going until it rolls over and dies?
19/09/2022 19:48:57 UTC
Ren - The Ed¹ said :-
I can't decide Ross. On the one hand if it's working why stop using it? On the other hand I'd like to get another 125 (or maybe 250) I can trust enough for touring on once more. Don't get me wrong the 500 is great for touring as our last trip has proven once more but being a common or garden greedy human I always want more.
19/09/2022 20:18:13 UTC
CrazyFrog said :-
I knew I'd convert you to the one true way eventually Ren, burning oil is the way forwards I tell ya! Welcome to the 2T club!

Sadly, I'm no longer a member though as I finally sold my Jawa on after 5 years of faithful service, and replaced it with this:-
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20/09/2022 08:53:52 UTC
Ren - The Ed¹ said :-
That's definitely not a Jawa and while it has 2 pistons it's a 4 stroke. I'm actually awaiting a write-up from a chap who's put 80,000 miles on his 'Zuma, I'll be interested to read that.

While my 125 is burning a lot of oil it still has the decency to be a 4 stroke, no "ring-a-ding ding ding" tinpot exhaust note here. Admittedly it rattles like a 2T, tickover is intermittent like a 2T and it's becoming unreliable like a 2T... but it's not a 2T!
20/09/2022 09:45:32 UTC
Upt'North ¹ said :-
I know you do it so we don't have to Leader. it time to shoot it through its heart. Do you want the 12 bore?
I do like that Zuma wotsit thingymabob. Very smart. It looks a proper motorsiccle.
20/09/2022 10:36:33 UTC
Upt'North ¹ said :-
80,000 miles on a 250. Wow, makes ya think dunnit.
I know there's no reason other than abuse and general wear and tear to destroy an engine. But even so, I'm impressed.
20/09/2022 11:07:22 UTC
Upt'North ¹ said :-
CF, I appreciate there would be a price difference, but is there any other reason you didn't go for a STrom 250?
20/09/2022 11:25:00 UTC
CrazyFrog said :-
I was looking at both Upt, but this 2016 Inazuma popped up on Facebook marketplace with 1500 miles on the clock and a full service history (5 stamps in the book!) for under £2k so it was too good to miss. Local to me too. First impressions are good.
20/09/2022 12:43:38 UTC
Upt'North ¹ said :-
20/09/2022 12:59:24 UTC
Ross said :-
Nice looking Inazuma CrazyFrog! Although I like my 500X I will always have a soft spot for my old Inazuma...very underrated bike I feel. I used to follow the owner's forum closely ( ) which sadly is very slow these days, but there were some high mileages racked up by some, mostly with very few problems! From my experience, the original chain is cheap and nasty, and you need to keep on top of any corrosion on the black painted collector box in the middle of the exhaust. If you jet wash the bike avoid the instrument pod as it can let water in and fog up the glass...have seen a few reports of heavy rain getting in too! Going up one tooth on front sprocket was probably the best mod' I carried out. Enjoy! :)
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21/09/2022 09:57:05 UTC
CrazyFrog said :-
Great, thanks for the tips Ross. I may try a 15t gearbox sprocket, but I have to say that every time I've tinkered with gearing in the past, I've always ended up going back to standard!
21/09/2022 14:13:06 UTC
Henrik said :-
Zuma is nice ,.. maybe my best bike ever

I mostly drive heavily loaded with luggage on the Zuma

So have my doubts about if the 15T is an good idea

Then again, its actually a bit greedy on fuel, so maybe,..

Question is what makes sense in my case

Ren Sorry for high-jacking the topic ;-)
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25/09/2022 22:02:59 UTC
Henrik said :-

A good seccond-hand offer on the latest model CB125F ,.. and maybe I will try out

But guess I will miss the Zuma-engine ,.. when heavy loaded in the Norvegian Mountains :-)

But the idea about a cheaper, more simpel, end fuel-ecconomic bike apeals to me these troubeled days

Would be cool if I could do it all with just a well-choosen 125 like the CBF in the long run
25/09/2022 22:16:27 UTC
nab301 said :-
Ren , nice piece of detective work on the sprag clutch! I think I'd change the battery or at least see what the voltage is doing when turning over the engine . Most of the sensors can be checked with a basic multimeter so that would be worth doing too.
@ crazy frog , lovely Inazuma , I looked at a similar fully faired one (before purchasing a DL 250 ) but it was too small for me in the tank/ knee interface area..
@ Henrik , The 250 Suzuki can be heavy on fuel if ridden hard and amazingly a Honda 500 can return better economy if ridden at 250 speeds, the deciding factor would be the purchase price and pay back over time plus licence restrictions, but a clean low mileage Inazuma for under £2k is a bargain.

26/09/2022 12:32:29 UTC
Ren - The Ed¹ said :-
nab301 - Thanks but I doubt my diagnosis was the result of intense and intelligent focused research, rather it was a result of luck with just a hint of knowledge about how things work on the CBF125. And regarding the poor running of the machine and blaming the electronics... there may be another (shameful) post coming soon about that.
27/09/2022 09:02:41 UTC
Snod said :-
I'm sure you know already, but if it's slipping (and has been slipping for a while) then it may have ruined the surface on the crankshaft and might never grip again. If so, can a kickstart be fitted? I see the Unicorn came with one, maybe the clutch cover and clutch are a straight swap..

Imagine the man points!
29/09/2022 23:55:16 UTC
Ren - The Ed¹ said :-
Thanks Snod and yeah...but I'm not quite sure. If, IF my vague recollections are correct I seem to recall the sprag rollers push against a protrusion on the back of the flywheel (aka the alternator magnet basket) and not directly on the crank.

However, no, I'll not be going to any great efforts to fix the starter or indeed find and install a kick starter from a random far eastern variant, no matter how butch, manly and heroic it may make me look. It's a 97,000 mile motorcycle that drinks oil. It's a 13 year old motorcycle complete with rust and corroded wiring and sagging suspension and broken panels and and and...

Anyhow it's running a treat and ticking over great now. Much to my eternal shame.
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30/09/2022 09:13:35 UTC
Snod said :-
Ahhh an interesting design choice, even easier to repair with a couple of used bits. Still, enjoy your bump starting if it comes to it :P

If you fitted a kickstart you wouldn't have to replace the battery either, just sayin'.
30/09/2022 14:02:29 UTC
Ren - The Ed¹ said :-
In the good old days of CDI units and carburettors then yes you can still run a bike with a dead battery using the kick start. When I was despatching both my CD200 Benly and CB250T Dream ate their batteries and I just kick-started them. Today however you still need a strong battery to power the computer, the fuel pump, the sensors and the injector(s) just to get it started.
03/10/2022 08:59:50 UTC
ROD¹ said :-
Yes Ren I thought the same as yourself, but!
I have been using a 12 v kettle for many years, in the works van, in the car, and yes on several bikes.
When trying this kettle on the 125 I found it was not boiling in the usual 25 minutes, so I pulled over to check.
The kettle was warm but not boiling.
I turned on the ignition, and nothing. No idiot lights were showing so my first thought was a blown fuse, but then I saw a dim light, and realized that the kettle was to much for the charging system and battery on the bike. I used the kick start, and the bike started instantly. So new bikes do start on the kick start with a flat battery.
03/10/2022 14:28:39 UTC
Ren - The Ed¹ said :-
ROD - What bike was that?
03/10/2022 16:07:44 UTC
ROD¹ said :-
Lexmoto Assault 125.
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03/10/2022 16:34:48 UTC
Ren - The Ed¹ said :-
Well I'll be damned! Let me think... I *would like* to say there was enough juice left in the battery to run the computer and injectors and ignition. However if you can barely see the lights then yeah, that's pretty darn flat I figure. So how are they doing it?

I figure - the kick has enough "ooomph" to spin the alternator sufficient to power the requisite parts enough to squirt and spark accordingly? Is it possible the computer has a backup battery and/or a very rapid boot time? No matter the answer it's a useful piece of information ROD.
04/10/2022 09:42:31 UTC
Crofty said :-
If your 125 doesn't make it to the 100k and you need another small tourer here is another recommendation for the Suzuki 250 in GW or DL form. Just back from 18 days touring on the dl250 a few days in Yorkshire but mostly in Wales.
Up to 16k now which is nothing compared to your 125. Bike still going great, heavily loaded with 30 ish kilos in luggage and me a 110k, 95 mpg when bimbling about the lanes and small roads, still go 74 mpg when I thrashed it back up the motorway to Scotland at 70. Great little bikes and if the 80k Inazuma is correct capable of big mileages too.
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06/10/2022 10:09:51 UTC
Crofty said :-

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06/10/2022 10:11:13 UTC
Ian Soady¹ said :-
Nice pics!
06/10/2022 10:23:44 UTC
Upt'North ¹ said :-
Nice pics Crofty.
Eds bike's never been that close to water....
06/10/2022 16:50:15 UTC
Upt'North ¹ said :-
P. S. How come you get a long rear mudguard on the 250.....or do you?
06/10/2022 16:51:24 UTC
Crofty said :-
Upt'North the DL250 came with that mudguard/rear bodywork. Think its standard. It seems to protect the rear wheel etc very well from mud/rain water. And like you i have a DL650 which shares oil filters and maybe other parts with it so it is a nice fit for maintenance.
07/10/2022 09:02:17 UTC
Upt'North ¹ said :-
Crofty, can't remember you saying you a had a STrom 650 before, but then again I can't remember if I put my pants on this morning. If you haven't already......we need pictures.
It's good news, just checked, I'm fully panted.

07/10/2022 09:50:25 UTC
Crofty said :-
Upt'North I have put pics of my 650 on here a couple of times, I have had the 650 3 years now. here are a couple of pics, not much imagination buy two red ones lol.
Glad your pants are all sorted
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07/10/2022 10:37:24 UTC
said :-

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07/10/2022 10:37:57 UTC
Upt'North ¹ said :-
Thanks Crofty, same model as The B then but in red. Nice.
Also been XT'd like The B. Nice again.
07/10/2022 11:05:35 UTC
Ren - The Ed¹ said :-
Blummin Suzuki owners clogging up the blog with their blummin Suzukis. If I were in the market for a 250 I'd be looking at the CRF250/300L or CRF250/300 Rally. Oh wait - tiny petrol tank on the Honda. Oh wait - tubed tyres on the Honda. Hmmmm... I wouldn't get a Suzuki would I?
07/10/2022 11:28:03 UTC
Crofty said :-
CRF is ok Ren but the DL beats it hands down for the road, being a twin its quicker,325 mile range against 110 for the crf, and have you seen the price of new ones, omg.
I did 15k on mine, trail riding in the Pyrenees and the Atlas mountains it was great but don't get me going on the 50/55mph average speed getting there and back not to mention looking for petrol 3 times a day. here's a couple of pics of mine.
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07/10/2022 19:15:33 UTC
Crofty said :-

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07/10/2022 19:16:37 UTC
Ren - The Ed¹ said :-
So that's what you look like Crofty! I can certainly understand the Suzuki 250s are much better road bikes than the CRFs, it's obvious to the eye as well as in the stats. How are you finding the 250 Strom's fuel consumption though? I know the CRF is frugal and that has caused me to cast an eye towards the CB300R which I have test ridden and rather enjoyed.
08/10/2022 09:44:15 UTC
Upt'North ¹ said :-
No Ed, that's Crofty's dad.
08/10/2022 11:42:51 UTC
Crofty said :-
Like I said before Ren the DL250 gets in the 90s bimbling about country roads 45/55mph, when you push on on m/ways and fast A roads it drops to the 70s. I usually go on to the last bar at 280 ish miles and can only get 12/13 litres in so usually about 21/22 miles to the litre. The cb300r is a bike I fancy too because of its light weight sub 150ks i think.
But it maybe doesn't have much of a sub frame and heavy touring luggage might be difficult so its out for me as i like to tour on both my bikes. I got about 90mpg with the crf250 but if I was pushing on or against strong winds or long inclines it dropped to the 70s as well.The Forza 300 I had never got more than 84mpg with me on board but its got a big frontal area and i'm 110kgs suited up. I think the Honds 300cc single is a great engine, the 350cc even better. If only they would make a cb350x with tubeless tyres and about 170kgs that would fantastic
08/10/2022 18:59:52 UTC
Marv said :-
Good to hear you found the cause of the strange issue. If the worst happened to my little CBF125, I think I'd now replace it with an ADV350!

Though I do also like what Honda have done with the current CB125F, seems to have some nice little upgrades.
19/10/2022 21:42:46 UTC

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