honda hornet starting issues when hot

hi there

I have a 2008 cb600f honda hornet abs model. I have owned the bike for nearly a year but recently having issues with starting from hot. battery is reading 12v and when running its 13.7v but if I turn off and start within a short period up to half hour it will seem like the battery is flat. ive put a meter on whilst it does this shows 12v as always try to start and drops to 5v. If you leave it to cool it will start up again or if I put the jump pack on starts fine every time hot or cold. I have had the battery checked which has come back all okay and its not an overly old one. Im now thinking could it be a starter fault causing this when its hot but have priced this up and at just over £900 inc vat I really am now hopping this isn't the case. Any feed back or help would be amazing thought id put the feelers out before I spend a ridiculous amount of money on a starter.

battery.

I'd agree with the above. Batteries should read above 12.5volt at rest. If the voltage is just 12v and dropping under load it's on its way out.

Hot engines have higher compression so they make more demand on the battery.

The fact that it starts fine with a boost from jump leads suggests it's the battery rather than the starter.

Do you ever use a trickle charger? Charging systems don't fully charge a battery to maximum capacity so they can often run at partial charge.

I'd agree with the above. Batteries should read above 12.5volt at rest. If the voltage is just 12v and dropping under load it's on its way out.

Hot engines have higher compression so they make more demand on the battery.

The fact that it starts fine with a boost from jump leads suggests it's the battery rather than the starter.

Do you ever use a trickle charger? Charging systems don't fully charge a battery to maximum capacity so they can often run at partial charge.

Absolutely got to agree with what has been said already.

Time for a new battery methinks.

So much cheaper than a starter motor lol.

Cheers

Ian

It might be worthwhile putting the battery on a conditioning charge if you have a suitable charger

Hi all

Thank you for your reply’s I have just put a brand new yuasa battery on it so not a cheap one and fired the old girl up lovely got to temp turn off to then 5 mins rest not start again battery reading 12.5v before starting and 14v while running then when tried to crank volts drop from 12.5 to 7v causing it not to start as if the battery was flat. Left it 30 mins to cool down and it fires up again. So fault is more than a battery and the same as before can’t quite get my head around it grrrrrr

There's a problem I've seen reported on a number of Hondas and existed on a Blackbird I used to have that's worth checking as it can give really weird symptoms. On the loom there's a common earth block that connects together all (many?) of the ground leads together routing them to the frame.

They tend to look like this and are generally wrapped in the loom tape somewhere...

They way they work is that all the ground (negative) wires go in to this block including the line to the chassis and then a common rail is inserted in to the back of the connector. Over time this can corrode and cause all sorts of weird issues. On my bike this manifested itself as the bike cutting out when hot and then refusing to start for a few minutes but other people have reported other problems.

The solution is to find the block, cut it off and then join all the wires together somehow. I did this by soldering ring connectors on all the wires and then joining them together with a nut and bolt finally wrapping it all in self-amalg tape back in to the loom. After I did this I didn't have another problem.

I'm not saying that this is your problem but it's a relatively easy thing to eliminate so it's not affecting any other tests you do.

Hi all

Thank you for your reply’s I have just put a brand new yuasa battery on it so not a cheap one and fired the old girl up lovely got to temp turn off to then 5 mins rest not start again battery reading 12.5v before starting and 14v while running then when tried to crank volts drop from 12.5 to 7v causing it not to start as if the battery was flat. Left it 30 mins to cool down and it fires up again. So fault is more than a battery and the same as before can’t quite get my head around it grrrrrr

Did you charge the new battery before fitting it?

Could this Possibly be a temperature sensor issue ?

Sounds like a connection issue or starter.

got to be heat related... connections on starter or starter related if its still doing it with a new battery, something is getting to hot.

but what do i know

A good read here might find your problem

https://www.knowyourparts.com/technical-resources/starting-and-charging/starter-will-not-crank-when-hot-heat-soak/

Heat soak is a common problem with a lot of motors, old corroded cables, weak starter solenoids, battery connection and finally the starter motor need to checked for conductance and resistivity.