Problems starting engine when hot - any troubleshooting tips?

[AKxx70]

Hi all CBF experts!

I have had my CBF1000F Mk2 2013 for a year now and what was originally a minor issue is now getting more and more frequent.

The engine struggles to start when it is hot. For example, I start the engine and go for a short ride to local shops. After getting back in about 10 min the engine is still hot and it fails to fire. It is spinning but not catching except for an odd misfiring attempt.
To recover I have to "blow" air by having throttle fully open while starting (fuel supply cut out). Sometimes it helps sooner, sometimes later. The battery gets dangerously close to a complete discharge. Sometimes I have to wait for 5 min with ignition turned off before re-trying. I was lucky to ride my bike back home so far but it may not continue for long.
To me this sounds like the engine gets flooded for whatever reason but I am not sure. Sometimes I sense a smell of petrol which is a sign of a flooded engine.

And another observation - the cold engine sometimes does not start normally too, even when the bike was not used for a few days. I have to "blow" it for 3-4 seconds keeping the throttle fully open and only then I can start it normally again. Was it flooded or not in this case?

I'd appreciate any ideas/tips before I start checking spark plugs!

[Art]

Sounds as if the air:fuel mixture is too rich and the engine is flooding. I've occasionally flooded my SC58, always on a cold start and most probably caused by condensation in the cylinder head or bores. Cranking the engine on full throttle has always seen it fire up sooner or later. I remember one time when it took ten or more repetitions of 5 seconds cranking on full throttle, 10 seconds rest, 5 seconds of cranking on closed throttle before it spluttered into life.

The spark plugs shouldn't be an issue other than to confirm the engine is running rich. NGK give the OEM spark plugs (IMR8C-9H) a 100,000 mile service life, however, if the engine has been running rich for some time their service life will be reduced.

Service history may offer some clues, for example: when was the air filter last replaced; are there any current or stored Diagnostic Trouble Codes (DTC) there's a how to read them here. Did you fit an after market exhaust and replace the exhaust servo motor with a proprietary eliminator?

Other causes of a rich air:fuel mixture, which should show up by way of a DTC, include failed or faulty: Manifold Absolute Pressure sensor; Intake Air Temperature sensor; Engine Coolant Temperature sensor; Exhaust Gas Circulation valve; Intake Air Control valve; Pulsed Air Injection Reed valve; Intake Duct Control valve; vacuum pipes.

[keithriley]

From the limited information given it sounds like you do a lot of short journeys. Have you, or do you ever, go for a decent blast giving the engine a good workout. The CBFs do have a lot of torque and can be ridden sedately, winding open the throttle to pick up speed, but do you ever take the engine revs higher up in the range ? One thing I was taught / shown in a Ride Safe course a few years back (and this is true of most riders) keep the gearbox in one gear lower than you normally would, thus keeping the revs higher. Predominantly done to aid control and pick up of speed, but also spins the engine up more. As an engineer I have a lot of mechanical sympathy but you also have to remember these things are designed to be ridden.

[AKxx70]

Originally Posted by Art

The spark plugs shouldn't be an issue other than to confirm the engine is running rich. NGK give the OEM spark plugs (IMR8C-9H) a 100,000 mile service life, however, if the engine has been running rich for some time their service life will be reduced.

The mileage is low, only 12K, so the plugs should be fairly new, I guess.

Originally Posted by Art

Service history may offer some clues, for example: when was the air filter last replaced; are there any current or stored Diagnostic Trouble Codes (DTC) there's a how to read them here. Did you fit an after market exhaust and replace the exhaust servo motor with a proprietary eliminator?

I will look for any possible DTCs... The exhaust is original.

Originally Posted by Art

Other causes of a rich air:fuel mixture, which should show up by way of a DTC, include failed or faulty: Manifold Absolute Pressure sensor; Intake Air Temperature sensor; Engine Coolant Temperature sensor; Exhaust Gas Circulation valve; Intake Air Control valve; Pulsed Air Injection Reed valve; Intake Duct Control valve; vacuum pipes.

Wow, that is a long list! :) Thank you!

[AKxx70]

Originally Posted by keithriley

From the limited information given it sounds like you do a lot of short journeys. Have you, or do you ever, go for a decent blast giving the engine a good workout. The CBFs do have a lot of torque and can be ridden sedately, winding open the throttle to pick up speed, but do you ever take the engine revs higher up in the range ? One thing I was taught / shown in a Ride Safe course a few years back (and this is true of most riders) keep the gearbox in one gear lower than you normally would, thus keeping the revs higher. Predominantly done to aid control and pick up of speed, but also spins the engine up more. As an engineer I have a lot of mechanical sympathy but you also have to remember these things are designed to be ridden.

Well, yes, I have done quite a few short journeys lately even though I did some longer motorway journeys too last year and I did not notice much difference in behaviour then. Will try a longer journey this weekend and try to pay more attention.
As for the revs - it probably sounds weird but I hate high revs and honestly this CBF has so much torque that I often cruise on the 5th gear at 30-40 MPH in town. Maybe it is a bad habit after all.

[keithriley]

Originally Posted by AKxx70

Well, yes, I have done quite a few short journeys lately even though I did some longer motorway journeys too last year and I did not notice much difference in behaviour then. Will try a longer journey this weekend and try to pay more attention.
As for the revs - it probably sounds weird but I hate high revs and honestly this CBF has so much torque that I often cruise on the 5th gear at 30-40 MPH in town. Maybe it is a bad habit after all.

I know what you mean but these bikes so quiet anyway I'd try riding around with higher revs. I'm just about to change jobs and go into engine development, I'm pretty sure there won't be any testing that involves the scenario you ride in, ie low revs, high gear.

[AKxx70]

Originally Posted by keithriley

I know what you mean but these bikes so quiet anyway I'd try riding around with higher revs. I'm just about to change jobs and go into engine development, I'm pretty sure there won't be any testing that involves the scenario you ride in, ie low revs, high gear.

I wonder why do they not make diesel bikes! 

[keithriley]

Originally Posted by AKxx70

I wonder why do they not make diesel bikes! 

They have, they did, can't recall why it's not a thing. Possibly because diesels tend to be long strokes and low revving

[AKxx70]

Originally Posted by Art

...
Service history may offer some clues, for example: when was the air filter last replaced; are there any current or stored Diagnostic Trouble Codes (DTC) there's a how to read them here.
...

Finally managed to get to the connector (not easy on Mk2) and read MIL blinks - it blinked only one stored code = "23"
According to the manual "23" means:

O2 sensor heater circuit malfunction
• Loose or poor contact of the O2 sensor heater connector
• O2 sensor heater or its circuit malfunction

Do you think this is related to the issue or is it not relevant?

[AKxx70]

A after having found code 23 I proceeded with as per the manual.
- Disconnected the O2 sensor and measured the resistance of sensor heater: was 8.4 Ohm i.e. within normal 6.7 - 9.5 Ohm range.
- Checked power supply voltage to the heater - was 12.2V - looks ok.

The remaining tests verify the sensor circuit towards ECM and require an ECM test harness which I do not have.

With the sensor cable disconnected I turned ignition on and MIL was blinking current code "23" straight away, so the cable issue was detected just fine.
I turned ignition off, then connected the sensor cable and checked the stored DTC codes again - it was code "23".

Tried to start engine - it started after a few attempts (as described in my original post).
I ran the engine for a few minutes, then turned the bike off. Then cleared the stored DTC codes from memory using the procedure in the manual.

Tried to start engine - and it started just fine despite the engine being hot. Not sure if this was a coincidence.

Put the battery on Optimate for the night - will continue troubleshooting tomorrow.