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Honda CBF 125 (Not Starting)

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Stingemore
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Joined: 09 Apr 2020
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PostPosted: 11:55 - 10 Apr 2020    Post subject: Honda CBF 125 (Not Starting) Reply with quote
Hi All,

Need some help please, I am stuck in the mud with trying to start my Honda CBF 125. Its been absolutely fine for the last couple of weeks until it started struggling to start, it would take a couple of attempts however when running, would be fine. Eventually a few days past and it began cutting out when the revs where low. Its now not starting at all. I will post the video link below, if you hold the throttle in the right position, it sounds like it attempts to start but fails. I have checked the following
Brand New Battery - Fully Charged
Eazy Start - No attempt to fire
New Spare Plug & Plug sparks outside head
Valve clearances double checked for both Exhaust & Intake side are set to the specified distance as per Haynes/Online
Fuel Replaced and topped to full tank
Injector is clean and spraying nicely
Removed Exhaust Temp - No change
Removed Intake Air Filter - No change
Piston Compression is fine
Oil is topped up and good
Spark Lead is working fine
TDC aligns perfectly with T on the flywheel
Replaced ECM with like-for-like model - No change
Check wiring loom, no frail cables anywhere
Fuel Pump pressures fine upon ignition and pumps fuel adequately into a pot

Video Here
https://www.youtube.com/watch?v=4qToB_gBuoQ

I'm stuck! Any help would be very much appreciated! Unfortunately Honda is shut so I can't speak to any technical specialist about this
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jaffa90
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PostPosted: 12:55 - 10 Apr 2020    Post subject: Reply with quote
Is the spark plug wet with fuel after all that cranking, also does the end of the exhaust smell of fuel and can it breathe?
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Stingemore
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PostPosted: 13:08 - 10 Apr 2020    Post subject: Reply with quote
jaffa90 wrote:
Is the spark plug wet with fuel after all that cranking, also does the end of the exhaust smell of fuel and can it breathe?


Hi Jaffa90,

I would say the spark plug is relatively dry and no smell of fuel at the end of the exhaust. I tried cranking before with the exhaust completely removed and it made no difference. I would expect the plug to be drenched with the amount of turning over its doing. I've had the throttle body off and its definitely spraying fuel through the injector.
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Riejufixing
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PostPosted: 13:47 - 10 Apr 2020    Post subject: Reply with quote
It the exhaust pipe actually on in that video clip? It sounds as if there's an entire panzer battalion clanking through your workshop.
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steve the grease
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PostPosted: 13:47 - 10 Apr 2020    Post subject: Re: Honda CBF 125 (Not Starting) Reply with quote
Stingemore wrote:
Hi All,


Eazy Start - No attempt to fire



As easy start will pretty well go up if you spray it around and 20 feet away some one lights a fag up, I will propose, that for one reason or another there is no adequate spark.

classic is > spray easy start down carb > bike runs for 3 seconds= no fuel getting to plug.

If easy start down carb > bike still makes no attempt to run= no spark.
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I've been riding, and fixing , bikes for 50 years, in that time the more I learn, the less I am absolutely sure of.....
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Stingemore
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PostPosted: 14:20 - 10 Apr 2020    Post subject: Re: Honda CBF 125 (Not Starting) Reply with quote
steve the grease wrote:
Stingemore wrote:
Hi All,


Eazy Start - No attempt to fire



As easy start will pretty well go up if you spray it around and 20 feet away some one lights a fag up, I will propose, that for one reason or another there is no adequate spark.

classic is > spray easy start down carb > bike runs for 3 seconds= no fuel getting to plug.

If easy start down carb > bike still makes no attempt to run= no spark.


Doesn't attempt to start with easy start or some fuel added directly into the bore. If you remove the spark plug and touch it against the head, its sparks good however I'm not sure its sparking at the correct time. The spark doesn't appear to spark with a regularly pattern, more of an erratic spark however I don't have another CBF 125 to compare the spark pattern outside of the engine.
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Riejufixing
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PostPosted: 14:49 - 10 Apr 2020    Post subject: Re: Honda CBF 125 (Not Starting) Reply with quote
Stingemore wrote:
I'm not sure its sparking at the correct time. The spark doesn't appear to spark with a regularly pattern, more of an erratic spark

If it's sparking properly when you turn it over it will go "click click click click click" regularly.

As I asked, are you trying to start it without the exhaust fitted on your video clip? If not, what's that terrible noise?
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Stingemore
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PostPosted: 14:58 - 10 Apr 2020    Post subject: Re: Honda CBF 125 (Not Starting) Reply with quote
Riejufixing wrote:
Stingemore wrote:
I'm not sure its sparking at the correct time. The spark doesn't appear to spark with a regularly pattern, more of an erratic spark

If it's sparking properly when you turn it over it will go "click click click click click" regularly.

As I asked, are you trying to start it without the exhaust fitted on your video clip? If not, what's that terrible noise?


Sorry, Exhaust is fitted securely in the video and the seat is off. The microphone is very sensitive in the Samsung so might sound louder than what is is. My issue is deffo pointing towards spark / timing....
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WD Forte
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PostPosted: 15:04 - 10 Apr 2020    Post subject: Reply with quote
Dont know the CBF but have fiddled with a YBR EFI bike on occaision

I see no mention of testing the crank sensor
or safety interlocks where say a faulty side stand switch will inhibit sparks
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Stingemore
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PostPosted: 15:24 - 10 Apr 2020    Post subject: Reply with quote
WD Forte wrote:
Dont know the CBF but have fiddled with a YBR EFI bike on occaision

I see no mention of testing the crank sensor
or safety interlocks where say a faulty side stand switch will inhibit sparks


Hi,

We tested the crank sensor yesterday with a Digital oscilloscope and its reading outputs from the flywheel as it should. Also did a continuity/voltage test from the CKP connector to the ECM with positive results so no broken cables. We are tempted to replace the CKP sensor as a test as there isn't much else that controls the spark timing as the ECM has already been replaced.

Side stand only stalls the motorbike when it enters first gear, shouldn't stop it idling in neutral. I have done a continuity check on the side stand and its reading the correct values with the side stand up/down.

Very odd this one, spent hours on it already...
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Stingemore
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PostPosted: 15:30 - 10 Apr 2020    Post subject: Reply with quote
- wrote:
Is it just me or does the starter sound a bit slow in that video?

Will it bump start?


Its spinning plenty fast enough to start, battery is also brand new and on a Optimate, no point trying to bump start.
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spottedtango
Trackday Trickster



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PostPosted: 16:32 - 10 Apr 2020    Post subject: Reply with quote
Have you checked the coils to see if the resistance is good?

My other thought was the crank sensor but that’s been mentioned. I had very similar problems on my 900ss and turned out to be that. It controls both timing of fuel and spark on my bike
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Riejufixing
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PostPosted: 16:48 - 10 Apr 2020    Post subject: Re: Honda CBF 125 (Not Starting) Reply with quote
Stingemore wrote:
Riejufixing wrote:
If it's sparking properly when you turn it over it will go "click click click click click" regularly.

As I asked, are you trying to start it without the exhaust fitted on your video clip? If not, what's that terrible noise?


Sorry, Exhaust is fitted securely in the video and the seat is off. The microphone is very sensitive in the Samsung so might sound louder than what is is. My issue is deffo pointing towards spark / timing....

Oh, ok. I wondered about some mechanical failure leading to an irregular spark, which I should have said goes "zap zap zap" not click, although that's the sounds it makes.
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Kawasaki Jimbo
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PostPosted: 17:02 - 10 Apr 2020    Post subject: Reply with quote
- wrote:
If it started by bump starting, you could rule out half that list.

How so?

I'd test or replace the ignition coil. The spark you can see might not be good enough.

Still, with that amount of cranking I'd expect to smell unburned fuel.

I'm not sure it's wise to keep cranking for that long, -something about overheating the starter motor.
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bypass2
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PostPosted: 22:12 - 10 Apr 2020    Post subject: Reply with quote
is petrol flow from the tap to the carb good or maybe the petrol tap or carb is faulty. try some easy start down the spark plug hole.
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Stingemore
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PostPosted: 23:15 - 10 Apr 2020    Post subject: Reply with quote
Tomorrow I will attempt to bump start so I can tick this off the list Smile

I am going to order a replacement Crank Sensor/Stator and Ignition coil tomorrow.
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Stingemore
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PostPosted: 23:24 - 10 Apr 2020    Post subject: Reply with quote
Quote:
Apparently all
Things needed are present, but clearly at least one of spark, fuel, air, compression and timing is not good enough to start from the button.

Bumping it might get it started. Then the OP can accept that one of their “checked that” clearly isn’t within tolerance.

At a guess, I’m going for compression.


I have already ordered a Compression test kit, just waiting for it to arrive. Will cross reference the values with the Haynes manual. Updates to follow Smile
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Stingemore
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PostPosted: 23:39 - 10 Apr 2020    Post subject: Reply with quote
Stingemore wrote:
Tomorrow I will attempt to bump start so I can tick this off the list Smile

I am going to order a replacement Crank Sensor/Stator and Ignition coil tomorrow.


Brand New Genuine Honda Stator Alternator Generator/Crank sensor ordered and Ignition coil, ETA delivery Thursday/Friday.
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Stingemore
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PostPosted: 11:05 - 11 Apr 2020    Post subject: Reply with quote
- wrote:
Stingemore wrote:

I am going to order a replacement Crank Sensor/Stator and Ignition coil tomorrow.


You see, this is the problem. You've listed a load of things you pretend to have tested, when you clearly have not.

In the opening post you claimed this.

Stingemore wrote:

Piston Compression is fine


Tell me how you you tested it without a compression tester?
It's impossible to try to help troubleshoot something when the OP lies about what they've already ruled out.


Your certainly living upto your name as you keep replying with the most stupid remarks, either provide useful help please or don't reply at all.

1, Compression - General compression test from A) Listening to the engine crank over sounds good B) Finger over the spark plug hole feels good. C) Initial observation looks good. Okay I don't have the "exact" compression reading value until my kit turns up but this is a good estimate. Values to follow !

2. There isn't much I can replace / alter the spark timing so that's why for good measures I have ordered replacements. I'll paste what I have already posted about testing the Crank sensor so you can re-read again if you missed it, or what you think i tested while sleeping as it's all lies.

Quote:
Tested the crank sensor yesterday with a Digital oscilloscope and its reading outputs from the flywheel as it should. Also did a continuity/voltage test from the CKP connector to the ECM with positive results so no broken cables. We are tempted to replace the CKP sensor as a test as there isn't much else that controls the spark timing as the ECM has already been replaced. 
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Easy-X
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PostPosted: 16:40 - 11 Apr 2020    Post subject: Reply with quote
Thumb over the spark plug hole says "I have some compression" but then I had some compression on my old DT... the head was bolted down barely more than finger tight Shocked it would start but not very well.

I would say for an engine not to start at all, not even a splutter, you would need one of the following:

Zero compression - even some compression you'd get something.

No spark - while you might get a weak spark in open air it might not be enough to get going in petrol vapour. I'd be looking to see the bright lightning of angry pixies rather than say a dull orange spark barely seen in bright sunlight.

Severe air/exhaust restriction - no flow, no go!

No fuel - if the plug isn't wet then either fuel isn't getting into the carb/injector or it's not getting out. A squirt of "Start Ya Bastard" is an easy test.

Timing - this would have to be massively out. Squinting at marks is all very well but just 'cos they're right it doesn't follow the spark plug is dancing to the same beat as the valves? Have you got a strobe gun?
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