It just stopped and no-one knows why

[Oakie]

Toodling down the highway last week and the bike ('92 Honda CB400SF) just stopped. No backfire, no rough running ... just wound down to a halt. (Yes, plenty of fuel in the tank.) I cranked it over but gave no indication of firing up again. I gave it about 10 minutes rest to think about it what it had done and then cranked it over and it fired up good as gold and we toodled on down the highway again ... for about a kilometer when we had the same stoppage. Cranked again to no immediate avail but after another 10 minutes waiting she started up, ran as normal... and we got another kilometer. Long story short ... we got it picked up but the mechanic at the shop we took it to has been unable to diagnose the fault. (They left it idling with the idea of seeing what happend when it stopped of it's own accord but of course it just kept on ticking over sweetly!) Naturally my first thought was the fuel supply but that seems OK. He's looking at the electrics but can't seem to find any faults.

Any ideas anyone?

[White trash]

Any ideas anyone?

Yup.

Trade it quick smart on a Gixxer.

[Motoracer]

Yup.

Trade it quick smart on a Gixxer.

There's a reason why you are in sales and not workshop, isn't there?

[White trash]

There's a reason why you are in sales and not workshop, isn't there?

Yup. I'm a mechanical spastic. And I've already worked in that department.

[Ixion]

Toodling down the highway last week and the bike ('92 Honda CB400SF) just stopped. No backfire, no rough running ... just wound down to a halt. (Yes, plenty of fuel in the tank.) I cranked it over but gave no indication of firing up again. I gave it about 10 minutes rest to think about it what it had done and then cranked it over and it fired up good as gold and we toodled on down the highway again ... for about a kilometer when we had the same stoppage. Cranked again to no immediate avail but after another 10 minutes waiting she started up, ran as normal... and we got another kilometer. Long story short ... we got it picked up but the mechanic at the shop we took it to has been unable to diagnose the fault. (They left it idling with the idea of seeing what happend when it stopped of it's own accord but of course it just kept on ticking over sweetly!) Naturally my first thought was the fuel supply but that seems OK. He's looking at the electrics but can't seem to find any faults.

Any ideas anyone?

Pretty much has to be either fuel flow or something related to temperature. No sign of overheating ? What happens if you ride slow at very low revs ? Do you get more than 1 km when starting from cold ? Tried taking the fuel cap off when it happens? Blocked vent pipe ? Dirty fuel? Dud coils ? . Sticky pivot on the CB (probably don't have one though) . Can you make it happen, turn off fuel and drop a carby bowl (assume this model has carbs of course. If its injected then it's any mans guess and probably a job for the experts) to see if there's fuel there. Make it happen, whip a spark lead off fast , stick it on a spare plug and check for spark . Older type bikes, if I had to look at one thing first it would be either fuel filter or coil. Later ones with electronic mumbo jumbo ? Call in the mumbo jumbo witch doctor

[Drunken Monkey]

Well I had 2 toyotas with the same symptom, it was the igniter both times. Don't know if your bike has an igniter before the coils though...

[2 schmoke]

thats exactly what happened to me the other day.. my bike just stopped.. i let it rest and it went well for 10 minutes then just stopeed again. so we took off the carburettor ( cant spell it) and looked inside and there was a shit load of crap inside.. which was evidently blocking the jets, so we cleaned that out ann i goes fine now

[Sniper]

My deduction is its broken

[Motu]

While it was stopped and wouldn't start - you did something important that made it go again....retrace your every movement.Did you pick your nose?,Which nostril,which finger of what hand? Witch way did you walk around the bike..clockwise or widershins? did you recite any incantions? It's all in the details - but somehow you did something that made your bike go again...recreate the actions and you have the first step into the magical world of motorcycles...

[BUBBLE]

Sounds like fuel, check filter and tank breather, try the fuel tap both On and Reserve.

Yep....go the Suzuki's.

[Oakie]

A week earlier it stopped on me after 1 km but then went fine for the next 300km. This time we'd done about 30km.
At the roadside I thought it had to be fuel. I turned the petrol tap off, took the bowl off the bottom of the tap and there was (clean) fuel there. When I turned the tap to 'on' and then 'reserve' no petrol flowed out from the tap which surprised me a little ... although perhaps it needs to be sucked rather than just flowing freely?
There were no signs of overheating. Liquid cooled and the needle hardly moved from the chilly end of the temp guage. No hot smell.
Thought it may have been electrics and something breaking down under load but the regularity of the distance between stopping still makes me think 'fuel'.

Blocked vent pipe creating a vacuum in the tank sounds interesting. I noticed the other day when it was sitting in the heat, the expanded vapours were venting from somewhere under the seat rather than the petrol cap which is where I'm used to it venting from. Hmm. Lunchtime. I might go and annoy the mechanic with that idea.
Cheers

[vifferman]

Blocked vent pipe creating a vacuum in the tank sounds interesting. I noticed the other day when it was sitting in the heat, the expanded vapours were venting from somewhere under the seat rather than the petrol cap which is where I'm used to it venting from. Hmm. Lunchtime. I might go and annoy the mechanic with that idea.
Cheers

Sounds like that could possibly be the fuel tap, if it's a vaccuum-operated one. If it is, and the diaphragm is bruk, it will leak and smell, as there's a small vent on the tap mechanism on the outside of the diaphragm chamber. It would also explain the bike stopping, as the diaphragm isn't being pulled out by the manifold vaccuum.

If it's not a vaccuum-operated tap, I dunno. :spudwhat:
But as others have said, venting's important. VTRs f'rinstance, have a habit of stopping if there's grunge in the end of the vent hose, as there's no fuel pump to force petrol through and a slight lacking in venting stops the thirsty big carbs getting enough juice - OK at idle, but not at road speeds.

If it's not fuel, then an electrical fault can often show up only when the bike's hot. An R/R or alternator fault seems most unlikely, as then the battery would be flat, but faulty coils often crap out when hot.

[Ixion]

I turned the petrol tap off, took the bowl off the bottom of the tap and there was (clean) fuel there. When I turned the tap to 'on' and then 'reserve' no petrol flowed out from the tap which surprised me a little ... although perhaps it needs to be sucked rather than just flowing freely?

Very suspicious that.I have known bikes that had a diaphragm on the tap so that the fuel didn't flow out in a crash. Could be your problem. In thory suction from the engine works on the diaphragm to open the flow (enough fuel in carb and tap bowls for initial start).

Diaphragm wrinkles/holes etc, won't open properly. Lets a little fuel flow through, enough for idling but with an open throttle the bowl on the carb empties after a while. Then you have to wait until the slow piddle getting through the tap fills the carb again

Definately sounds like fuel , get a mecho to check the tap (or bypass it temporarily)

[vifferman]

Very suspicious that.I have known bikes that had a diaphragm on the tap so that the fuel didn't flow out in a crash. Could be your problem. In thory suction from the engine works on the diaphragm to open the flow (enough fuel in carb and tap bowls for initial start).

On my VF500 I had problems with the tap in that sometimes the No.1 (or whatever) cylinder whose intake manifold it was connected to would run REALLY rich as it sucked extra fuel directly from the tap. And every so often, the hose would crack (petrol going into it probably didn't help) and it would run extra lean.
Stupid bloody thing...

[Riff Raff]

My deduction is its broken

My deduction is that it doesn't love you anymore! Have you been giving it lots of TLC prior to the event, have you told it that you love it recently, have you given it a nice warm garage to sleep in? If the answer is yes to all these questions, then it's a cantankerous bitch and needs to be traded on a Gixxer (do I get commission for helping you with a sale White Trash??)