Losing engine at traffic lights


Hi All,

Sorry, another day another thread…

Was on my usual commute this morning, 25 miles each way on north circular.  Around 15 miles in today, stopped at traffic lights, waiting for the lights to change in first gear, clutch pulled in as normal when the engine just died.  No spluttering or anything, just dead.

Tried to restart, nothing happened, no turnover, oil light and ABS light on.  I quickly checked kill switch, felt for kickstand, couldn’t see any issue so threw on hazards and wheeled to side of the road. Luckily all before lights changed.

After about a minute of trying, suddenly all started fine, bike started, oil light turned off and finished ride into work with no issues, including stopping at several more lights.

Bike is 2012 Hornet, new battery and regulator rectifier a few weeks ago.   Once at work I checked the kill switch seems fine, the side stand doesn’t seem loose, and the oil was topped up to the maximum.  Temperature on whole route was between 70-105 degrees which is usual for my bike.

Any suggestions on things I need to look at?  Should I ignore and assume it was a bad bit of fuel or anything unless it happens again?  Or should I get my arse straight to a garage and hope it is nothing serious? 

I just spent a grand on the bike with battery issues, new tires, service etc, so really don’t want to spend any money, but safety first.  



New battery?  Check your battery connections are nice and tight!  That could well be the issue.



Would that cause the engine to die?  I thought battery would just affect starting it, not actually make it stop?



Exactly the same thing happened to me last year with my Street Triple. Even started up again just like you, and then the bike behaved as normal. I called the dealer and they said it was most likely fuel - a bit of dirt or something. No problems since. 



I know from GSRs that they would stall sometimes when pulling clutch, traffic lights or when changing gear. Two things to check are the idle speed, and TPS (and secondary) TPS adjustment. Some GSR users were reporting those causing issues.

With something like this, I would start with the simple stuff first. Wait to see how often it happens. Once, it could be something like poor quality fuel… if it happens regularly, then look progressively at the easiest thing. Idle speed you should be able to check without much effort. The switches (and any gunk around them) on the clutch & sidestand probably can be done at same time.

From my experience, it’s one of those things that you need to eliminate one thing at a time.

For now, I wouldn’t worry too much, unless it happens again… 



Wiring issue with the kill switch?



its a known trait for BMW F models to stall when coming to a stop from a constant speed 

its all down to fuelling, BMW set the F up to run lean the side effect of it is a stalling engine & one that doesn’t like to tick over , BMW have tried to cure it by introducing new fuel mapping but haven’t totally eliminated it.

Me I played with the tps &  air temperature sensor and im happy with the results.  



Sidestand switch?


Would that cause the engine to die?  I thought battery would just affect starting it, not actually make it stop?
Admittedly I know nothing, but I thought the battery triggers the spark plug, to ignite the engine, to charge the battery, to trigger the spark plug?


Would that cause the engine to die?  I thought battery would just affect starting it, not actually make it stop? RyanSimmons
Admittedly I know nothing, but I thought the battery triggers the spark plug, to ignite the engine, to charge the battery, to trigger the spark plug?
My knowledge is that when I turn the twisty thing that makes the wheels turn.  OMC course is the limit of my bike knowledge really.  I really need to do a proper in depth maintanence course.

Sidestand switch? brains_t
I was thinking the same thing, I know that on Suzuki SV650's they can have a problem where the sidestand or clutch switches can fail which would cause the same issue. 


If a mechanical novice, one very useful.advice is to know when the bike has won and it’s time to get someone who knows a bit more to look at it. Especially for something like this, without knowing how everything works and what it’s supposed to do, you can end up screwing up things to the point where you create a bigger problem than you had.

As mentioned, see if the problem happens again. Bikes do have one off hiccups as there’s loads of different parts that have to work at the same time and occasionally they can freak out.

If it happens again, check the small things. If that doesn’t fix and is now happening regularly, get it to a trusted mechanic or mechanically minded friend.


Sidestand switch? brains_t
That's the first thing that came to my mind too.


Well commute home and back in was fine.  Only weird thing, and I am not sure if I am being paranoid is that after getting home I turned engine off, then tried to restart and I had to wait 10 seconds or so.  Until then the start button did nothing and sounded like a loud fan was running.  (Not the normal whine when you turn on the ignition, rather a full blown fan for a few seconds.)  This morning started within 1 second or turning the key.

Will see if it is fine on way home otherwise will drop into garage tomorrow.

On a separate point, drive safe out there guys.  My commute is A406 and as of yesterday pass 2 “Fatal collision, information wanted” signs each way with bikers killed in the last few weeks.  Along with yesterday seeing a biker down near Ealing with paramedics treating.  He looked all right, was sitting up with oxygen and they were treating his leg, but still scary.



I’m not sure what would cause the engine to cut off in the first place, but the other symptoms of non-starting when the engine is warm sound a lot like my sticking starter motor. Might be worth crossing the starter relay and starter motor off the list of things to check.



No mention of the red ignition light in the original symptoms. The red ignition light is the only light to be concerned with when diagnosing this type of electrical fault. Its controlled by the ECU and comes on and goes off depending on the charging system voltages. The normal condition is for the red ignition to come on with the ignition and go off when the engine is running and the alternator is charging the battery.

Since recent work included battery issues check the battery. Check that the battery is of the right specification, check the battery terminals are secure and not damaged, check the battery’s level of charge and check the charging system output voltage. That’s about all you need to do.

The loud fan running will be the radiator fan kicking in because the coolant  temperature sensor has told the ECU that the coolant has reached that temperature where the fan needs to be triggered. Its perfectly normal for the fan to kick in when the mo’cycle is stationary and the engine is running. The fact that the starter motor failed to crank the engine while the fan was running may be a clue here. The engines ECU will shut down if the battery voltage falls below a preset voltage. So if the fan kicked in and the battery voltage fell below the preset voltage under load that could have been enough for the ECU to shut down. Depending on what circuits the ECU is programmed to shut down under such circumstances you may still get all or some warning lights show.

Intermittent faults are a technicians nightmare, some will even refuse to attempt a full diagnosis if the described symptoms are too sketchy. Other than checking the battery as above I’d just wait and see if the fault repeats itself. I’d not even bother to check the likes of clutch switch, side stand switch, kill switch, tilt switch etc. Do make and keep reference notes of exactly what happened, when it happened and the circumstances at the time.