Camchain and tensioner seen up close in a cutaway bike engine

Home Repair And Restoration

Bump Starting A Modern Motorcycle Is Hard

Bump Date 31 May 2020

By Ren Withnell

I haven't seen Sharon for 10 weeks. We finally met up this Sunday for a socially distanced ride out as restrictions ease during the lockdown. 

Eh what? In case you don't know Sharon and I don't live together. Sharon's daughter just before lockdown had just been under the knife for brain stem surgery, perhaps the most dangerous surgery going. Said daughter is still recovering and Sharon needed to be strictly isolated to ensure her daughter didn't receive Covid 19 through her. 

Now the daughter is on the long, long long road to recovery and her immune system is starting to recover. While we can't start snogging and hugging Sharon feels confident enough to meet up and ride as long as we keep apart, from each other as well as the populous.

We stop atop a steep hill near Longridge, Jeffrey Hill. We talk for about half an hour then mount up to depart. Sharon's battery is flat. Either there's something amiss or she's left the ignition on and on a modern bike that means the lights are on too. Dagnammit.

This isn't the first time this bike has had a flat battery. Last time it was my fault, partially. We'd used her bike to charge the powerpacks that charge the mobile phones and having charged her 10,000 mA pack and my 10,000 mA pack there wasn't enough left to start the bike. See Of Batteries and Glendaruel for more details.

Would it bump start back then? Hell no! 

You see a modern motorcycle doesn't just need lots and lots of very angry electrons to turn the starter motor. It needs spare suitably miffed electrons to pressurise the fuel pump too. Oh and to operate the fuel injector. Don't forget the computer wants its own electrons as well but these need only be rather grumpy. I had to go and purchase some jump leads to get the indignant and furious electrons out of my bike and into Sharon's. Of course today I don't have my jump leads.

A et of jump leads on the back box of Ren's motorcycle
Jump leads. Perhaps a modern motorcycling essential?

What I do have is a very steep hill. What Sharon's bike has, apparently, is an awful lot of compression. First gear, the rear locks up. Second gear, the rear locks up. Third gear, the rear locks up. This is a long steep hill. I really really do not want to walk back up it.

Fourth gear and the motor turns but does not start. Why? I suspect I'm going to have to get the furious electrons from the alternator and not the battery. I let the speed build through gravity, dump the clutch and let the motor spin. A lot. A very lot.

It catches and fires - hooraah!

But this reaffirms the lesson. To bump start a modern motorcycle you can't do it "old skool". You on the bike, your mate pushing it along the car park, that won't get enough revs for long enough to get the electrical juices flowing. You're going to need a steep long hill. 

Or jump leads or one of them jump starting power packs. 

After another 50 minutes on the road we stop for tea from our individual flasks and eat our individually prepared butties at an approved distance. The bike starts just fine. Sharon had noted after the event that she was riding faster, much faster. Ahh, yes, the computer has defaulted to KPH not MPH. 

Ren's 500 and Sharon's 250 at the roadside on a warm day with blue skies
Both bikes working fine now, although the bikes might not be 2 meters apart.

Was it the lights? Or was there a loose wire that got nudged? We need to check this. I also need to habitually pack jump leads just in case.

Wise insights or lessons learned through muppetry, click here to share your knowledge (or lack of therein)

Reader's Comments

Ian Soady said :-
If this is a common occurrence it may be worth devising an "ignition on but bike not running" warning buzzer. You already have an ignition warning light - you could put a timing circuit in to sound the buzzer if the ignition was left on for say 5 minutes. Or you could fit something clever so that the lights only come on when the battery is being charged. Or you could fit a switch to turn the things off.

Of course those of us with magneto ignition don't suffer from this kind of thing. Lots of other things of course....
01/06/2020 12:04:45 UTC
Bogger said :-
Been there done that. It wasn't a particularly modern bike A 1997 VTR Firestorm. 3 Big blokes pushing it. Absolutely no chance of it starting. Got it going via jump leads and a kindly motorist.

Last time was 2yrs ago in Welsh Wales in February. A group of us had stopped the weekend at a pub/hostel.
Came to go home on Sunday and a mates 2017 BMW GS was completely flat.

Luckily one of the other lads, on an SH300, Had a set of jump leads with him. The mighty SH got the GS going again no problem.

Turns out it was one of those small cigarette type USB chargers, was drawing current, even though nothing was plugged into it.

I subsequently bought a quality small set of jump leads from a car boot sale. £1.00 well spent.

01/06/2020 12:07:23 UTC
Upt'North said :-
We'll never know?
I wouldn't have thought dirty earth connections on a new'ish bike would be an issue but a loose one might be. Of course motorcycle batteries are tiny little holders of electrical energy and they can soon drop out of the sweet spot. It could be with lack of use it might be on its way to battery heaven although I presume it's been plugged into a tender? Not always a good thing.
Bump starting any modern vehicle seems to be just about impossible for all the reasons you suggested.
I think the small booster packs seem impressive but just another thing to pack/forget.
Hopefully Madam Sharon just left it switched on and it'll be fine now, run it and see, but remember your cables.

01/06/2020 13:00:38 UTC
Bill said :-
Some engine ECU have a minimum voltage requirement for the FI so if below do not trigger. As I have optimate plugs on my bikes I made a lead with mail plug to connect to optimate plug on bike and crocodile clips at the other, not a jump lead as such but connected to a running vehicle, bike or car it only takes a short time to put enough into to bike battery to top up and can also be used in the opposite direction from optimate plug to croc clips on another flat battery, small and light to stash in bike.
01/06/2020 13:07:31 UTC
Ren - The Ed¹ said :-
Ian - it must be obvious to all the readers I am a mechanical expert (obviously) but when it comes to electronic circuitry I am, frankly, clueless. I wouldn't know where to start wiring up a 5 minute timer. I could fit a switch to the lights though. Ideally I'd like to fit LED bulbs as the drain is considerably less. Hmmmm.

Bogger - I do have a set of "small" jump leads which are suited to the less powerful starter motors on a motorcycle. I just need to remember to put them in my top box.

Upt' - I dare say the battery might a) be getting on a bit and b) wasn't helped by our, erm, my draining it in Scotland. Fickle things batteries. The one on the CBF must be at least 9 years old and is as happy as larry although it gets regular use which lead-acids seem to appreciate. I've had them go bad after 2 years as well so go figure.

Bill - I didn't know that about ECUs but it makes sense. It's trivial for an electronics expert (not me) to create a voltage monitor and a few lines of code in the computer. The battery on Sharon's bike is not readily accessible so some connector that can manage a handful of amps may be the ticket.

Thanks folks, it all helps.
01/06/2020 16:44:53 UTC
Snod said :-
So did she leave the lights on or did it die 30 minutes after being parked up? It might be worth checking if it's charging okay, mine gave similar symptoms when the stator burnt out.. And yes they really are difficult to bump!
01/06/2020 17:13:06 UTC
nab301 said :-
Get yourself a mini power pack I guess , you can use it as a powerbank to charge phones etc too .
01/06/2020 18:57:40 UTC
Ren - The Ed¹ said :-
Snod - we stopped for a good hour during the next break and the bike started fine. This would *imply* (not guarantee) that the charging system is working OK. Might be worth waving a multimeter over it though.

Has anyone reading got one of those power banks that can (allegedly) jump start even a diesel? It all sounds just a little too good to be true but then technology does move on. Who'da thunk I'd have a mobile phone that does sat-nav, internet, emails and, yes, honestly, even make phone calls!?
01/06/2020 19:56:57 UTC
nab301 said :-
I don't have one but I have access to them through work. If you look at the spec of the very small ones that would be suitable to carry on a motorbike , they only push out about 160 to 200 cca cranking amps for 5 seconds so these ones would not be suitable for diesel imo and are only recommended for medium size petrol engines... Also, all of these products generally have polarity protection which requires a certain minimum voltage on the vehicle battery before they can "power up " otherwise the vehicle would require a trickle charge from a running vehicle to raise the battery voltage.
01/06/2020 20:29:52 UTC
Bogger said :-
I think you are better off with jump leads personally. Said BMW owning mate from my previous posting pulled one out from under his seat with a smug look on his face. Connected it to his battery, pushed the start button and CLICK. No start.

As long as you have a slave battery jump leads are always going to work. With a battery start pack you don't know if it will work until you come to use it.

I have used the small start packs to jump start vehicles and if they are in good nick they are amazing. I have started a BMW 5 series 3.0 ltr diesel with one and the starter pack was about the size of 4 packs of fags. However three months later it was goosed and and would not start anything. It wasn't a cheap one either.

02/06/2020 06:47:51 UTC
Ren - The Ed¹ said :-
I did wonder if those jump starting power packs are a bit like the trite you get off TV Adverts. They "do the job" as stated on the packet but either not very well or not for long. Just enough to avoid false advertising claims.

In the meantime jump leads but I'll look into fitting maybe some high current connector too as getting to the battery on the Z250SL is not BAD but it's not a 2 minute job.
02/06/2020 08:24:17 UTC
Borsuk said :-
I have 300 amp ones for the bikes and 500 amp ones for the cars as they are all diesels. Used them a couple of times over the years with success. They are cheap enough that I put one with each vehicle.
I had a standard 12v battery one in my car in Spain. Last time I had to use it there was nada power, even though it had been charged up a week or so before. I took the back cover off and that’s when I found that the battery connections to the leads were basically 1mm thick bits of copper which had corroded through.
Personally I wont jump start a car or bike unless my engine is off. In fact where possible I will disconnect one of my leads. Modern vehicles have so much electronics in them that starting another engine with your own running can fry the electronics. When you start your own engine your electronics are protected from the high load while you are cranking. When you jump start another car this protection doesn’t apply as its part of your cars starting sequence.

I fried a company cars brain jump starting a colleague one night. The company were not impressed and the bastard drove off leaving me stranded.
02/06/2020 08:50:19 UTC
Upt'North said :-
I'm with Borsuk here and also our Ed.
Vehicle electronics are complex and very expensive and I really don't understand how the components are or aren't affected by connecting jump leads or connecting via the SAE leads to another slave vehicle.
I only know there's a thousand YouTube videos telling you how to kill either yourself or the vehicle if you're inclined to try.
I do believe the safest way to do it would be with a power pack from a reputable source on't interweb thingymabob and used in accordance with the manufacturers instructions.
I'm sorry if I've come over all serious, it won't last long, but if you fry your innards you've probably just written off your pride and joy.
I have never used a power pack Ed, but from the BeaST forum they get good write ups and many say they have started there V8 behemoth without hesitation or issues. I also think that as more people tour with more electrontrickery then a good powerpack with the right connections could be a cost effective solution.
02/06/2020 09:47:40 UTC
Upt'North said :-
Yes, I'm sorry Ed, they do cost money, you'll get over it. Maybe.
02/06/2020 09:50:38 UTC
Upt'North said :-
Like this....
Posted Image
02/06/2020 09:54:34 UTC
Bob said :-
Bill mentioned about ECUs being fussy about voltages.
I very much doubt you'll get a BMW (I flippin hate BMWs) to start like this, on some models the minimum voltage it will work is 11.5V, below that and it just won't fire the coil or injector.
The Keihin fuel injection system on the Kawasaki is very forgiving I find (it's probably identical to the one on my KLX).
I've wired up a service switch to the headlight on the KLX, so that I can have the ingition on without sacrificing the 5A that the headlamp wants.

02/06/2020 11:27:47 UTC
Bob said :-
I don't have a problem putting jump leads on any vehicle. Electrons is electrons.
Just double and triple check that you have the correct polarity.
You'll see advice about conneting the 0V first or the +12V first - it makes no difference whatsoever. The only reason you might want to connect the +12V first is that if you connect the 0V first you will then have a +12V lead flapping around waiting to short onto your frame or engine.
If you're careful handling the leads there is no problem.
02/06/2020 11:40:09 UTC
Bill said :-
The way to stop frying the electronics when jump starting is that once the vehicle with the flat battery is running, turn on as many consumers as possible headlights flashers, heated grips all of what you have.Now remove the jump leads ,alway negative first, now turn off your consumers one at a time, this acts as a buffer and the charge output is progressive. It's not the battery that frying the electronics as it can never put out more than its rating, so 12v battery circa 13v max 12v electronics will have a higher peak protection. The issue is the alternator if you just pull off the jump leads your charging system goes from seeing a good battery (the slave)to a flat battery (yours) instantly which cause a huge spike that kills electronics. I worked in the truck industry and we had measured 900v spike on 24v alternator, although this occurs for mille seconds the damage is done.
Also always run the slave vehicle at revs for a short time to put some charge into the flat battery before trying to start.
02/06/2020 11:40:20 UTC
Upt'North said :-
Bob and Bill, that's all good advice and the routine I would follow, but.........
What if there's no other vehicle? Head scratch.
02/06/2020 12:47:52 UTC
Bill said :-
Phone a friend Upt, don't think I can run fast enough to bump start the BWS though :-)
02/06/2020 22:49:30 UTC
Ren - The Ed¹ said :-
I daresay I'm more confused than ever. Jump starting may or may not kill my electronic system and/or Sharon's electronic system. Power packs work but maybe not, it depends. I'm sure if we had more readers there'll be stories of how the power pack killed the electronics too.

At some point I will have to form my own thoughts and come up with my own solution. I don't doubt for one moment each and everyone's experience is valid and true, it seems we all have suffered and enjoyed different experiences. Much like medicine we are conditioned to believe science offers a RIGHT way and a WRONG way to do things but the real world is way way more complicated than that.

I'm thinking now I need one of those starting rollers that they use for the moto-gp, my own portable "steep hill". Or... right... how about a long chain. I put the bikes rear to rear with a long 520 chain from my output sprocket to Sharon's, then use my engine to bump start Sharon's engine, or vice versa. We'll also need a paddock stand for Sharon's bike (no centre stand). Apart from the dangers of a 14 foot long chain suspended in thin air I can't see a problem.
03/06/2020 08:58:47 UTC
Upt'North said :-
"Phone a friend Upt'"
Ah, that's my problem then. Billy no mates..........
03/06/2020 09:09:51 UTC
ROD said :-
I think there may be a logical solution to the problem.
Its called a kickstart!
03/06/2020 09:48:50 UTC
Upt'North said :-
I don't miss kick starts.
Blooded ankles and shins come to mind.
03/06/2020 10:43:31 UTC
Ren - The Ed¹ said :-
No I think ROD is right on the money there. My old CB250T's battery failed sometime around the 40,000 mile mark but it had a kickstart. I never did replace that battery. Started easily off the kicker and I was despatching it back then so it got a lot of starts.

Of course, as bleeding ever, it's not that simple. The CB250T had CDI ignition which is self powering. It had no fuel pump either. Or computer. Dagnammit!
03/06/2020 13:23:11 UTC
Bill said :-
Ren, rear wheel to rear wheel will achieve it without flailing chains and lost body parts BUT no electrickery = no eletronicy = no start
Stick to jump leads but put remote connection if access to battery is poor, you only need positive as you can always find a good accessible earth engine bolt etc.
03/06/2020 13:37:00 UTC
Ren - The Ed¹ said :-
Rear wheel to rear wheel. Hmmmm. If we can get it spinning fast enough the alternator should provide the angry electrons. SHARON! We need removable numberplates and tail lights.

Good call on positive only access to the battery, yes the negative can go through the frame. Simples.

Aaaah...problem with the wheel to wheel. My wheel would turn Sharon's wheel backwards. Sussed. We need a portable idler wheel which would also negate the need for removable numberplates and tail lights. Hmmmm...
03/06/2020 13:42:02 UTC
Bill said :-
Ren, rear wheel to rear wheel will achieve it without flailing chains and lost body parts BUT no electrickery = no eletronicy = no start
Stick to jump leads but put remote connection if access to battery is poor, you only need positive as you can always find a good accessible earth engine bolt etc.
Or something permanent on both bikes as per link and carry a lead
03/06/2020 13:42:44 UTC
Ian Soady said :-
In the old days of course we would (well I wouldn't) tie two Belstaff belts together and use them as a towrope for a tow start. Or just tow the offending bike home.

Alternatively (and this may well not work) start the running bike (bike A) then remove the battery and fit it to the non-running one (bike B) while keeping bike A ticking over. Then fit the dead battery to bike A.

This may of course fry your delicate electrics.....

Rear wheel to rear wheel - surely that would drive it in the wrong direction?

And Up t' - you were obviously doing it wrong. Like much else technique is everything.
03/06/2020 13:45:47 UTC
Snod said :-
Rear wheel to rear wheel sounds like a genius idea to me, not sure why the esteemed engineers on there seem to think it'll spin the wrong way??
03/06/2020 14:51:49 UTC
Ian Soady said :-
I wondered who'd be the first to notice that one Private Pike.

Yes of course you're right. Glad to see someone's brain is working....
03/06/2020 15:04:06 UTC
Bill said :-
I think you will find it goes the correct direction Ian, common trick with off road bikes.see the video
03/06/2020 15:05:39 UTC
Ren - The Ed¹ said :-
I stand corrected (and I have orthotic shoes to prove it). Yes of course wheel to wheel would be fine, durgh! Looks like I'll have to source those removable rear ends then.
03/06/2020 15:21:38 UTC
Bill said :-
Other rear wheel uses are available if not recommended
03/06/2020 15:48:15 UTC
Ren - The Ed¹ said :-
If a scoot can do that Bill imagine the g-forces you could achieve with a Hayabusa. Might have a contender there for SpaceX.
03/06/2020 16:38:32 UTC
Bob said :-
You won't get away with removing the battery from a running bike if it's EFI.
The battery smooths out the full wave rectified AC from the alternator. Without it the voltage will fall below the minimum required for EFI functions at the intersection between the falling wave from one alternator phase and the rising wave from the next.
On bikes designed to run without a battery there is a large capacitor fitted to perform the smoothing function.
04/06/2020 09:44:48 UTC
Ian Soady said :-
Just a thought - does Sharon stop the bike with the kill switch? It's easy to leave the ignition on if you do this. In my opinion kill switches are the work of the devil.

Some years ago when I'd just bought my Triumph Tiger 955i my brother came over and of course had to take it for a ride. He returned an hour later with the tyres smoking and the engine crackling so I tucked it away till the next day. When I went to start it, it would turn over fine but wouldn't fire. After stripping off side panels etc etc and looking for a bad connection my eyes finally alighted on the kill switch. Which was of course in the off position.

I also understand that some EFI systems - the Tiger included - don't do a clean shut-down if they're stopped using the kill switch although I have no direct evidence for this.

Bob - my suggestion was made somewhat tongue-in-cheek although the capacitor solution may be a solution. My Norton Commando had a huge blue capacitor which allegedly made it possible to start with a flat battery although I never put that to the test.
04/06/2020 10:29:39 UTC
Bob said :-
I can claim to be a bigger idiot than you.
My first bike was a GP100 - it was lots of trouble.
Given the bike's difficult history I was thinking the worst when it wouldn't go one day.
I got as far as having the piston in my hand before I noticed the kill switch!

I think I'd prefer to have on though. I tend to run my bikes without "B" throttle cables and although I've never had a throttle stick open I like the idea of an emergency cut off.

And thinking on I do occasionally use my kill switch when in severe distress in off-road activities!
04/06/2020 11:06:26 UTC
Bob said :-
Sorry Ian, Just read that back.
I am not trying to call you an idiot - it was an awkward turn of phrase I wish I hadn't used.
04/06/2020 11:07:45 UTC
Ian Soady said :-
No trouble Bob and no offence. I've been called worse!

I can see the value on an off-road bike, in fact remember once competing in a long-distance trial on Exmoor when I managed to trap myself under the Bullet with the engine racing and the throttle jammed against the bank. The decompressor which Enfield had chosen to fit rather than a proper valve lifter did nothing but fortunately another competitor was close behind and lifted the bike off me so I could close the throttle. But for on-road use I think I'd probably be able to reach the ignition switch as fast as the kill switch even if I remembered that it was there.
04/06/2020 11:13:18 UTC
Ren - The Ed¹ said :-
Kill switch! Get with the times gentlemen please. When stopping on a hill it is always advisable to leave the motorcycle in gear, particularly as motorcycles lack a hand brake (save for automatic DCT Hondas now). As such Sharon would likely have followed my instruction "Leave it gear!" when we parked on the slope.

On a steep hill, on a somewhat gravelly surface and being short int' leg it is safer for hobbitses to simply push the side stand out while in gear. This cuts the motor via the side stand switch while allowing her to keep both hand on the bars. As we were only stopping to chat and catch up we weren't leaving the bikes hence no reason to remove the key (thus not turning off the ignition and lights).

While I'm not 100% sure this is what happened it is the most likely scenario. I myself rarely stop the bike, neutralise it and then turn it off at the key. My (bad) habit is to simply put the stand out, the bike is nearly always left in gear.
04/06/2020 19:56:53 UTC
Bob said :-
Sidestand switch?
First thing I removed on the KLX.
04/06/2020 20:47:18 UTC
Ren - The Ed¹ said :-
I understand the sidestand switch could be an issue off-road. Darn handy under most circumstances tho.
05/06/2020 08:39:02 UTC
Ian Soady said :-
I've never noticed a problem without one despite almost all my bikes missing this "vital" feature. They can however be yet another source of embarrassment as on the occasion when I parked the Tiger (again) in a field to spectate at the Red Marley hill climb - highly recommended by the way.

I left it in gear for the reasons mentioned. On the Tiger, that sidestand (or prop stand as we used to call it) switch allowed the starter motor to turn but cut the ignition, and as I remember you needed to pull the clutch in to start under all circumstances. So there I was being watched by all and sundry while the engine just refused to fire. Eventually someone strolled across and pointed out my error.......
05/06/2020 09:45:03 UTC
Ren - The Ed¹ said :-
Back in the good 'ole days my Hondas had side stands with a little bit of rubber on them. I wondered and pondered and questioned their purpose in life, their raison d'etre. Then you learn that if you go around a left hander with the side stand out this little bit of rubber causes the stand to flick up *JUST* before the side stand digs into the tarmac and spits you off highside.

This is what side stand switches are for. They live in the worst of the weather and all that the front tyre throws at it, thus at times they can fail and leave you pondering what is amiss with your bike. But I wouldn't be without one myself as I have experienced the effects of leaving the stand down.

However - as you state Ian some are "wired" rather frustratingly.

My Honda WILL crank and start in neutral on the side stand. As soon as the neutral light goes out it cuts the motor though. The bike will not crank if it is in gear with the stand out, clutch or not. This seems to be the best "setup".

Sharon's Kwak is the same but the Keeway will crank in neutral but not start with the sidestand out. As such there have been several occasions where we have declared the bike "dead" only to realise the stand is out.
05/06/2020 10:09:15 UTC
Bob said :-
It's worse than that Ren, on the KLX to release the full power map in gears 4,5 & 6 I've also had to link out the clutch switch.
So you can start my KLX in gear and on the side stand if you want!

I think I read somewhere that some new bikes won't run with the sidestand down at all, neutral or not368 - that is just silly.
05/06/2020 11:46:45 UTC
Borsuk. said :-
Seems silly to me as well as they tell you to warm the bike up before riding so you are standing there astride the bike for 5 mins doing nothing apart from look a plonker, and how are you supposed to fault find or check the bike when its running if you have to be sitting on it at the time. You shouldn't have to frigg out safety systems just to do basic checks. I’m lucky as my bikes all have centre stands but that is a rarity nowadays.
06/06/2020 10:38:54 UTC
Ren - The Ed¹ said :-
Bob - Sharon's Keeway will crank over but not start with the side stand out. I suspect the switch simply grounds the coils or CDI.

Borsuk - Warm the bike before riding? I don't recall that being the advice for a long long time. I always give the bike 15 seconds to ensure the oil is flowing then take it easy but ride the bike as normal. There are countless opinions on the "correct" warm up procedure, I might write up my thinking on this soon. I do my safety checks before I start the bike.

Wait - you didn't get this advice from a ship engineer did you? Them's big engines on the ship maybe they need 5 minutes to warm up.
06/06/2020 20:19:14 UTC
Borsuk said :-
Na, not from a ginger, actually says it in my owners manual.
Ships engines, main problem with stArting them is getting condensation out so they usually turn over with the no compression first to clear moisture out. Normally any initial manuevers are at slow speeds anyway which is not a problem. When going from manoeuvring revs to full sea speed You normally increase revs over about an hour to allow Even warming up of the system. The reverse when coming from sea speed to manoeuvring revs.
Best bit is when you go through the critical rev range when the engine hits its harmonic frequencies and the whole ship starts shaking. One ship i was on, a motor ship, was so bad that lights and aerials used to vibrate off of the main mast and shatter on the deck below. We used to refer to it as honeymoon revs.
07/06/2020 01:13:48 UTC

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