Bike cutting out at high speed

[cbfb]

Got a weird problem with my bike (GSF250) that neither myself or the local bike shop can quite put a finger on.

It had been struggling at high revs for a while, most noticeably it was bogging down at around 110 (9000rpm) and wouldn't go any further, maybe up to 120 if you were lucky. Then a couple of times it just cut out completely at around 100ish as if it had run out of fuel - sputtered, slowed down and eventually cut out. Left it sitting for a few minutes then it would start up again (primed it first not sure if that made any difference).

Anyway, I checked the fuel lines, fuel tap, filter etc, the obvious stuff but made no difference. Had no bloody idea by this point so took it to the local shop - they noticed a problem with the choke sticking on, also a suspect fuel line (had gone a bit soft and they reckon it had kinked). Picked it up last night, was running heaps better, straight up to about 130... 140... wouldn't go above that (not sure what these should do, that's as fast as it's gone so far).

Thought the problem was all fixed, feeling pretty happy then it bloody dies again, exactly like it had run out of fuel (yep I did check that!). Came to a stop, left it a few minutes then back to the shop again. I had been sitting on about 130 for a couple of Ks before then... My theory is that it uses up whatever's in the carbs at this speed then runs out of gas because it can't refill the bowls quick enough - some sort of restriction to the fuel flow somewhere (which explains why it's OK at slower speeds when demand is less) - but WHY????

The bike shop are scratching their heads, they've already cleaned the carbs and they changed an o-ring in the fuel tap today but can't make it break down again, meanwhile I'm paying them to ride around on my bike! Nice work for some :facepalm:

Am picking it up again tonight but have a funny feeling it's not gonna be long before it dies again... So does anyone have any ideas what to look at next? I'm stumped and it sounds like the shop is too at the moment :violin:

p.s. Yeah I will get a bigger bike but got a few months till my Full licence, on 6R atm.

[Flip]

Check the fuel tank is venting properly and not forming a partial vacuum.

[ducatilover]

Bring it over, I'll thrash the fuck out of it or something.

[nzspokes]

Check the fuel tank is venting properly and not forming a partial vacuum.

I agree. My guess is fuel tank not venting also.

[maggot]

Check the fuel tank is venting properly and not forming a partial vacuum.

That'd be my guess too. Next time it happens, pop the fuel cap and see if it's difficult to open, or makes a sucking sound when you open it.

[DrunkenMistake]

Check the fuel tank is venting properly and not forming a partial vacuum.
+1


Bring it over, I'll thrash the fuck out of it or something.
yah it will be wheelie wheelie fun..


I agree. My guess is fuel tank not venting also.

Do you have a tank bag?
I have herd of them suffocating the fuel cap on some bikes that chock it

[hayd3n]

check you breather hose

[FJRider]

Check the filter ON the fuel tap (inside the tank) is not clogging up with shit in the bottom of the tank. A trail bike I once had did that ... relined the tank ... SORTED ...

[darkwolf]

I'm assuming there is no noticeable smoke when it starts to cut out (suggesting an air shortage).

Otherwise, I'd be inclined to look at an air lock in the fuel tank. Recently heard a story about the breather valve on a new triumph being installed backwards let air out not in... Very similar symptoms. Bike shop was also stumped.

[cbfb]

Well, got it back from the shop last night and done about 50k back home then to work this morning, been really good actually. Overtaking is no longer a buttock-clenching gamble as to whether the bike will cut out as you run out of road approaching a truck, zips past really confidently now.


Bring it over, I'll thrash the fuck out of it or something.

Back in the shed you, I want that hand and bike fixed by 10th Dec so we can do the coast to coast :Punk:


Check the fuel tank is venting properly and not forming a partial vacuum.

I had a look at the tank cap and couldn't figure out where the vent was :facepalm:

The shop has apparently checked it but wouldn't mind double-checking, any ideas where I'd find the vent?


I agree. My guess is fuel tank not venting also.

As above, don't know how to check the vent is working?


That'd be my guess too. Next time it happens, pop the fuel cap and see if it's difficult to open, or makes a sucking sound when you open it.

Yep tried that, it was fine. Also tried taking the tank off the bike, then seeing if petrol came out slower/faster with the cap open/close - apparently that will tell you if there's a problem with the vent? Anyway, it was fine.


yah it will be wheelie wheelie fun..

Bwahahaha


Do you have a tank bag?
I have herd of them suffocating the fuel cap on some bikes that chock it

Nope, want one though


check you breather hose

Do you mean on the tank? There's an overflow outside the fuel cap but nothing on the inside that could allow air in/out.


Check the filter ON the fuel tap (inside the tank) is not clogging up with shit in the bottom of the tank. A trail bike I once had did that ... relined the tank ... SORTED ...

Yep, checked that... I replaced it 6 months ago when I rebuilt the top end, looks pretty good to me.


I'm assuming there is no noticeable smoke when it starts to cut out (suggesting an air shortage).

Otherwise, I'd be inclined to look at an air lock in the fuel tank. Recently heard a story about the breather valve on a new triumph being installed backwards let air out not in... Very similar symptoms. Bike shop was also stumped.

Nah no smoke, yeah I reckon the air lock sounds the problem, but would that explain why it only happens at high speed? I guess if there was only partial flow then it would cut out when demand got high?

[ducatilover]

I still think I should thrash it for you.

I'll do my best to get my hand and bike fixed, or swap the Corolla for another bike?

If it was a tank vent problem, it'd make perfect sense.
Have you raped the shit out of it in all gears?
If it's working now, just cross your fingers and hand me the keys.

[Scouse]

ride slower then it wont cut out

[Stirts]

Being the awesome knowledgeable mechanically minded person that I am :shifty: .........

Where do you get your fuel? This one time, when I fuelled up at Gull, my Hornet 250 run like puss-nuts. Coughed and spluttered and cut out.

Stopped using it and bike became normal again. :blink:

[cbfb]

I still think I should thrash it for you.

I'll do my best to get my hand and bike fixed, or swap the Corolla for another bike?

If it was a tank vent problem, it'd make perfect sense.
Have you raped the shit out of it in all gears?
If it's working now, just cross your fingers and hand me the keys.

What sort of bike are you gonna get for the Corolla? If you go with that idea I'm riding infront, there will be shit falling off it all over the place :facepalm:

Aye, so where is the bloody tank vent? I should bring it over, unless you're in barmy Palmy today?

Yeah I bring it close to the redline in all gears on the way to work, it's been OK.

Yep will see how it goes... Yeah sure, there will be a 3 grand deposit though


ride slower then it wont cut out

:done:

[cbfb]

Being the awesome knowledgeable mechanically minded person that I am :shifty: .........

Where do you get your fuel? This one time, when I fuelled up at Gull, my Hornet 250 run like puss-nuts. Coughed and spluttered and cut out.

Stopped using it and bike became normal again. :blink:

I usually get Caltex gas... Funny you should say that cause the shop filled it with BP and it's gone OK since then... maybe I should try using BP from now on... actually i boycotted BP so it will have to be Shell. Might be the way to go.

[DrunkenMistake]

What sort of bike are you gonna get for the Corolla? If you go with that idea I'm riding infront, there will be shit falling off it all over the place :facepalm:
My Hyo.


Aye, so where is the bloody tank vent? I should bring it over, unless you're in barmy Palmy today?

There should be an overflow hose, this will act as a breather too, or if you open the cam of your tank there will be a small hole on the outside of the filler hole

[ducatilover]

What sort of bike are you gonna get for the Corolla? If you go with that idea I'm riding infront, there will be shit falling off it all over the place :facepalm:

Aye, so where is the bloody tank vent? I should bring it over, unless you're in barmy Palmy today?

Yeah I bring it close to the redline in all gears on the way to work, it's been OK.

Yep will see how it goes... Yeah sure, there will be a 3 grand deposit though




I'd ride a GN250 at this rate :facepalm: there is an older model CBR600 in Palmy that I'm tempted to look over.
I'll sell the wondrous 'Rolla :yes:

I should be home, throw me a text if you're heading over. Really should do some more work on the bike.

It's not an air leak/jetting problem if you are able to wring the shit out of it now.

Cheque's in the male.

[cbfb]

My Hyo.

There should be an overflow hose, this will act as a breather too, or if you open the cam of your tank there will be a small hole on the outside of the filler hole

I've got a Galant I'd swap for it, goes well :innocent:, had a dodgy head gasket replacement, doesn't use any oil (coz it's all in the radiator) and someone lost a bolt that holds something important in place

Yep, there's a small hole on the outside of the cap that runs into an overflow hose. Have squirted that with compressed air, all good. But I can't see how that lets the tank breathe, as it's outside the cap seal? Feel free to tell me if I'm being thick.


I'd ride a GN250 at this rate :facepalm: there is an older model CBR600 in Palmy that I'm tempted to look over.
I'll sell the wondrous 'Rolla :yes:

I should be home, throw me a text if you're heading over. Really should do some more work on the bike.

It's not an air leak/jetting problem if you are able to wring the shit out of it now.

Cheque's in the male.

DO IT... If you would rather have the rust bucket than a CBR600 you need your head testing ... send me some pics, I might go buy it myself

Might pop over after work, will see what time I get off. Like going home via the track though :)

[ducatilover]

I've got a Galant I'd swap for it, goes well :innocent:, had a dodgy head gasket replacement, doesn't use any oil (coz it's all in the radiator) and someone lost a bolt that holds something important in place
It was an extra bolt :innocent: one of those unneeded things, probably a head bolt or a very grooved gudgeon pin.






DO IT... If you would rather have the rust bucket than a CBR600 you need your head testing ... send me some pics, I might go buy it myself

Might pop over after work, will see what time I get off. Like going home via the track though :)

Will make the Corolla nice and rust free, then sell it.
Just make the ride home extra long? That's what I'd do, then I'd crash.
You don't have to crash though.

[DrunkenMistake]

Just punch a hole in the top of the tank with a screw driver.
Problem fixed.


And my Hyo isnt worth a Rolla .. I mean cmon its a Hyo! haha

[cbfb]

Lord, how I've missed KB :facepalm:


It was an extra bolt :innocent: one of those unneeded things, probably a head bolt or a very grooved gudgeon pin.

Will make the Corolla nice and rust free, then sell it.
Just make the ride home extra long? That's what I'd do, then I'd crash.
You don't have to crash though.

Will do if it plays up again - for now though you really should get back in the shed or get that CBR.

It's like a different bike now, have to watch myself as it's considerably quicker...


Just punch a hole in the top of the tank with a screw driver.
Problem fixed.

And my Hyo isnt worth a Rolla .. I mean cmon its a Hyo! haha

Nah, with my insane lean angles the gas would piss out.

Oh wait, I'm mistaking myself for someone that can actually ride

[FJRider]

I usually get Caltex gas... Funny you should say that cause the shop filled it with BP and it's gone OK since then... maybe I should try using BP from now on... actually i boycotted BP so it will have to be Shell. Might be the way to go.

Actually ... the problem may even BE a gas station ... Over the (many) years I have had issues with water in the station tanks ... picking it up (along with other shit) when the tanks are low.

[darkwolf]

In theory, the bike should shit fart and piss itself once the tank pressurises regardless of speed. What it may mean is that the breather hose or one way valve is only slightly open. Theory being:
Travelling at 60KM/H in top gear might require 10% flow. Tank can breath 20%. 100KM/H may require 30% flow. After a period of time, bike dies because it can't get fuel (pressurises).

Is it possible to ride without the fuel cap on? Probably not a great idea safety wise etc but might answer your question.

[robinm]

If you are fueling up at the caltex in your ( and my) home town, that MAY be your problem. I started fuelling up in Ashhurst when the local was closed and noticed my car seemed to run better and got better milage. I have heard the same thing from a few locals now.

[cbfb]

In theory, the bike should shit fart and piss itself once the tank pressurises regardless of speed. What it may mean is that the breather hose or one way valve is only slightly open. Theory being:
Travelling at 60KM/H in top gear might require 10% flow. Tank can breath 20%. 100KM/H may require 30% flow. After a period of time, bike dies because it can't get fuel (pressurises).

Is it possible to ride without the fuel cap on? Probably not a great idea safety wise etc but might answer your question.

That sounds similar to what I was thinking... but no I'm not keen on riding without the fuel cap closed, the commute is pretty twisty so I would end up with a crotch full of fuel.

I see your point though, if it does it again I might see if I can bung it somehow but leave a hole, then take it for a blat down a straight. Unfortunately it's very inconsistent.


If you are fueling up at the caltex in your ( and my) home town, that MAY be your problem. I started fuelling up in Ashhurst when the local was closed and noticed my car seemed to run better and got better milage. I have heard the same thing from a few locals now.

Well I need to fill up tonight so I'll stick some dodgy Woodville gas in and see what happens! Maybe it's just like the water round here!

[Fast Eddie]

didnt really read any of the other comments, just butting in sorry.

I had a similar problem on my cbr250r, it would cut out at open road speeds as it wasnt getting enough fuel, it would use up whats in the carb and then die, you leave it to sit for a while until gravity does its thing and it would go again. Bike shop never fixed the prob. I had the tap etc all cleaned out. In the end I fixed it by swapping it with another tank off a running bike. So yea. it was something to do with my tank despite being cleaned etc, must be something in the fuel tap, the actual pipes in the tank, or maybe like i saw someone mention, pressure problem? not sure.

also how rusty does it look inside ur tank? I think mine was so so. It was a very long time ago tho.

[cbfb]

didnt really read any of the other comments, just butting in sorry.

I had a similar problem on my cbr250r, it would cut out at open road speeds as it wasnt getting enough fuel, it would use up whats in the carb and then die, you leave it to sit for a while until gravity does its thing and it would go again. Bike shop never fixed the prob. I had the tap etc all cleaned out. In the end I fixed it by swapping it with another tank off a running bike. So yea. it was something to do with my tank despite being cleaned etc, must be something in the fuel tap, the actual pipes in the tank, or maybe like i saw someone mention, pressure problem? not sure.

also how rusty does it look inside ur tank? I think mine was so so. It was a very long time ago tho.

Tank is pretty clean. Tap is spotless, fuel line is brand new. Only thing I can think is the cap.

Not done it for a few weeks so hoping the problem has gone away...

[SMOKEU]

Where do you get your fuel? This one time, when I fuelled up at Gull, my Hornet 250 run like puss-nuts. Coughed and spluttered and cut out.

Stopped using it and bike became normal again. :blink:

Are you sure the Gull fuel didn't have ethanol in it?