bike suddenly stops under acceleration ..

[pete.keys]

... just got back from a ride and a combination of pushing and riding for the last 5 miles.

Its a really wierd problem any suggestions ... symtoms below

Bike runs great normally - obviously

Last time I rode it, pulling hard onto a motorway slip road the revs suddenly dropped like the ignition was cut, then at slower speed - below 70mph it was ok but as I picked up the speed again the same thing happened. This happened twice so I cruised home under 70mph.

I went out for a run today and the problem has got worse. It ran ok for 7 miles to the local shops .. below 70-80mph all the way. I stopped for 30mins and then rode back .. after about a mile the ignition seamed to cut out. It wouldn't start straight away. I left it for a few minutes whilst I kicked myself for not having the tool role under the seat. Then it started again.

On the way home the problem got worse and at slower and slower speeds.

In the end I ended pushing the bike as it would stop, I'd wait for a while, it would start .. run for a bit then cut out... and then the battery gave out.

It isn't like fuel starvation where a bike sort of stutters to a halt... its like electrical failure .. but if it fails why would it start again and why originally worse it worse under load.

It seams electrical? But the horn and starter were turning ok? Yet again as the battery got flatter so did the distance between it stopping

any suggestions greatly appreciated ....

-Pete

 

[Rob Farmer]

It thought it sounded like the carb diaphragm initially. It could be the bean can giving up the ghost, if it is and you don't mind stripping one down I have a new, unused hall effect sensor you can have. I guess the obvious thing to do is swap it over with the one on your other bike.

I trapped the wire from the bean can between the timing case and the outer cover a few years ago. When it got hot the bike cut out, let it cool down and it would fire up again. When I got home and took the cover off you could see where I'd trapped it.

 

[Mr K]

I had an Austin Maestro van that did that It was a cracked distributor cap. Took ages to find.

Dunno if that helps.

 

[ghiribizzo]

Water in the float bowls?

 

[pete.keys]

It thought it sounded like the carb diaphragm initially

might explain why its getting worse. Some else has mentioned the coil breaking down.

I guess the carb diaphragm is easiest to check

 

[pete.keys]

I guess the obvious thing to do is swap it over with the one on your other bike.

I trapped the wire from the bean can between the timing case and the outer cover a few years ago. When it got hot the bike cut out, let it cool down and it would fire up again. When I got home and took the cover off you could see where I'd trapped it.

Thanks for the bean can suggestion - rings a bell with things I've read in the past- I'll cool down from the pushing - have a beer - and then go and have a check and swap them over. Already put the bike on charge when I rolled it into the shed

 

[Timpo]

With the tank off, there is the bank off electrical components on the right of the upper frame spar. I found the plug coming from the handlebars had corrosion on the pins and sockets, this was giving a similar effect as you mention. But my fault eventually prevented the bike starting.

T

 

[(RIP) pastyman]

would also check the petrol cap vent. If the vent is blocked it will cause a vacum in the tank preventing the fuel flow. It may not be completely blocked so will allow slow speed running but cut out when more fuel is required. Stop for a while and the effect will diminish and the fuel flows again. took me ages to find some years ago.
Just go for a ride with the tank cap loose and see if it still happens.

Worth a try

 

[John Armstrong]

Float levels ok?

 

[Flipfly]

I had very similar symptoms with Bertha. Turned out to be the wire to the coil was loose!

Worth a check before you go doing something drastic. I world have expected all sorts of popping and banging, but she just progressively lost power and the cut out. Restarted a number of times and the died properly. 5 minute fix with the aid of big brother (cheers Si).

 

[brassmonkey001]

It does sound very similar to what mine does when the fuel level gets low - it'll run but you can't open the throttle fully. It seems to me like the float bowls can't fill up fast enough.
It's weird because the fuel level isn't down to the petcocks so it's not actually going on to reserve but will do soon.

I have had trouble with fuel evaporation in the past so check your fuel line's are routed correctly. Mine had the fuel filter resting on top of the barrels so were getting a bit warm.

Still not got to the bottom of my problem though...

 

[MickDB1]

I would checkout the fuel lines - get yer bowls off and let it run into a container -see if it stops / slows down
Check the vent overflow hole in yer carb

 

[(RIP) Proff]

I would checkout the fuel lines - get yer bowls off and let it run into a container -see if it stops / slows down
Check the vent overflow hole in yer carb

I'm with Mick on this..
If you've only got one tap, you can easily use it faster than it can fill float bowl..
DAMHIK !!!

 

[Steptoe]

I'm with Mick on this..
If you've only got one tap, you can easily use it faster than it can fill float bowl..
DAMHIK !!!

Lets think about this........... Pull the fuel line off the tank and open the fuel tap. How long before the tank is empty .....

Now are you saying the bike will use fuel at the same rate as it pouring out of the tank unchecked while travelling at 70-80mph. Which means refilling the tank every 20 minutes. Which mean in 20 minutes (lets say half an hour for conveniance) you'd have travelled 40 miles and used over three gallons of fuel.

What you really meant to say is perhaps the floats are wrongly adjusted.

 

[cookie]

blocked main jet, or float level too low, for whatever reason?

 

[Roger Chatterton]

Have a look at the coils - some earlier coils got hairline cracks. Happened on my airhead RS a few years back. Damp gets in, and coils become intermittant.

 

[Popell]

Don'tr know what bike this is on and if,therefore this is relevent, but I had similar symptoms in a car and on my Thundercat- it was ice build up in the carbs.
Would run from start then as it got colder and the speed was up, ice formed, bike stuttered then eventually stopped, couple of minutes the heat soak from the engine removed the ice for a while then it would reoccura couple of miles down the road.

my 2d

 

[brassmonkey001]

Don'tr know what bike this is on and if,therefore this is relevent, but I had similar symptoms in a car and on my Thundercat- it was ice build up in the carbs.
Would run from start then as it got colder and the speed was up, ice formed, bike stuttered then eventually stopped, couple of minutes the heat soak from the engine removed the ice for a while then it would reoccura couple of miles down the road.

my 2d

Unlikely to occur on a Boxer though. eh?

 

[(RIP) Proff]

Lets think about this........... Pull the fuel line off the tank and open the fuel tap. How long before the tank is empty .....

Now are you saying the bike will use fuel at the same rate as it pouring out of the tank unchecked while travelling at 70-80mph. Which means refilling the tank every 20 minutes. Which mean in 20 minutes (lets say half an hour for conveniance) you'd have travelled 40 miles and used over three gallons of fuel.

What you really meant to say is perhaps the floats are wrongly adjusted.

O wise and benovolent GURU StEptoe...

My flow was very restricted, due to a load of fecking gunge blocking the wire screen round fuel pipe in the fecking tank
I finally got wise to it when it would not go above 75 mph, 2 up....and die like a dodo on hills
Like a fecking speed restrictor it was

 

[Popell]

Unlikely to occur on a Boxer though. eh?

Quite possibly, but I didn't think it would happen on the Thundercat seeing as the carbs were behind the engine AND the radiator.

I guess my caveat re the relevency was appropriate but we were casting about for possible causes.

To paraphrase Sherlock Holmes, if you have eliminated all possibilities but one, then you have found the culprit, however improbable it may seem.