Fuel Cap Breather

[darrsi]

Been looking around the internet and not found much, but was wondering if there's a  breather vent or hole that can be cleaned or poked on the fuel tank cap at all?

[joebloggs]

Been looking around the internet and not found much, but was wondering if there's a  breather vent or hole that can be cleaned or poked on the fuel tank cap at all?

Is the tank not vented from underneath, when I cut the bottom of the tank out I seem to remember two brass/copper tubes connected from the bottom to the pressing that the fuel cap bolts to, I guess one is the overflow and the other the vent.

[sc0ttie]

The hole under the fuel cap on mine got clogged a couple of months ago, cleaned it out with a long bit of single core wire and blew down it using a drinking straw. Not sure if that is what you mean though.

[darrsi]

I know there's a hole that goes from the top of the tank to the bottom vent underneath, but was wondering if there was anything in the cap at all that could need a clean.
To be honest it doesn't really matter now, i just found a shiny brand new one for £20 so thought i'd tart the bike up a bit as the old one looks so grubby.
It'll mean another key but i'm not really bothered about that. 

[fazersharp]

I know there's a hole that goes from the top of the tank to the bottom vent underneath, but was wondering if there was anything in the cap at all that could need a clean.
To be honest it doesn't really matter now, i just found a shiny brand new one for £20 so thought i'd tart the bike up a bit as the old one looks so grubby.
It'll mean another key but i'm not really bothered about that. 

Now i do like shiny - but what is so bad about the old one, wont it clean up

[darrsi]

I know there's a hole that goes from the top of the tank to the bottom vent underneath, but was wondering if there was anything in the cap at all that could need a clean.
To be honest it doesn't really matter now, i just found a shiny brand new one for £20 so thought i'd tart the bike up a bit as the old one looks so grubby.
It'll mean another key but i'm not really bothered about that. 

Now i do like shiny - but what is so bad about the old one, wont it clean up

Just looks old and a bit battered, and £19.99 delivered is not exactly breaking the bank.

[fazersharp]

I know there's a hole that goes from the top of the tank to the bottom vent underneath, but was wondering if there was anything in the cap at all that could need a clean.
To be honest it doesn't really matter now, i just found a shiny brand new one for £20 so thought i'd tart the bike up a bit as the old one looks so grubby.
It'll mean another key but i'm not really bothered about that. 

Now i do like shiny - but what is so bad about the old one, wont it clean up

Just looks old and a bit battered, and £19.99 delivered is not exactly breaking the bank.

This is what I would do

Drop allen key on tank - and chip tank.
Drop old filler on tank - bigger chip.
Drop new filler on floor - and bust it
Put old filler cap back on.
Spend 1 hour looking for the last bolt that the garage fairies have hidden.
Think - well that was a good 3 hours and 19.99 spent.
On top of that its now raining and I could of spent that 3 hours out on the bike

[Fazerider]

This is what I would do

Drop allen key on tank - and chip tank.
Drop old filler on tank - bigger chip.
Drop new filler on floor - and bust it
Put old filler cap back on.
Spend 1 hour looking for the last bolt that the garage fairies have hidden.
Think - well that was a good 3 hours and 19.99 spent.
On top of that its now raining and I could of spent that 3 hours out on the bike

                
I've had days like that too.

[darrsi]

I know there's a hole that goes from the top of the tank to the bottom vent underneath, but was wondering if there was anything in the cap at all that could need a clean.
To be honest it doesn't really matter now, i just found a shiny brand new one for £20 so thought i'd tart the bike up a bit as the old one looks so grubby.
It'll mean another key but i'm not really bothered about that. 

Now i do like shiny - but what is so bad about the old one, wont it clean up

Just looks old and a bit battered, and £19.99 delivered is not exactly breaking the bank.

This is what I would do

Drop allen key on tank - and chip tank.
Drop old filler on tank - bigger chip.
Drop new filler on floor - and bust it
Put old filler cap back on.
Spend 1 hour looking for the last bolt that the garage fairies have hidden.
Think - well that was a good 3 hours and 19.99 spent.
On top of that its now raining and I could of spent that 3 hours out on the bike

Got a tank cover on there now, so just the cap that's exposed.
I must say it feels much nicer now, the padding gives a better grip and i noticed a big difference in warmth as well not having the legs touching bare metal.

[darrsi]

The hole under the fuel cap on mine got clogged a couple of months ago, cleaned it out with a long bit of single core wire and blew down it using a drinking straw. Not sure if that is what you mean though.

I just tried using compressed air to blow down the air vent hole in the actual fuel tank and it didn't sound like anything was going through, but in fairness i couldn't see what size the hole is because of the rubber housing which surrounds it?
Which also makes me wonder how that hole can get clogged in the first place when it looks fairly protected?

[locksmith]

I suppose the obvious question is what makes you think it's blocked?

[Oldgit]

Canny Pee.

[darrsi]

I suppose the obvious question is what makes you think it's blocked?

Still getting the occasional starting issues, just a process of elimination.
Used a can of air at first, then popped by work to pick up a parcel then used a proper airline.
Read that extreme weather can cause issues if the tank isn't vented properly, as in very hot or very cold.
Got a new cap on the way but as i can't determine what the vent hole looks like due to the rubber part surrounding it, it was a bit of an unknown if it's right or not.
Blew air through the tiny cap hole underneath and i could feel air coming out of the cap mechanism so that's probably okay.

[locksmith]

As a lay-man, I would think a blocked breather would cause the tank to gain a negative pressure so that when you open the filler cap a loud hiss of air rushing in would be apparent. Is that the case?

[darrsi]

As a lay-man, I would think a blocked breather would cause the tank to gain a negative pressure so that when you open the filler cap a loud hiss of air rushing in would be apparent. Is that the case?

I think if it was totally blocked it would do that, but if it was that bad it would also run like shite or even cut out.
Once it's started, eventually, it appears to run okay though. I'm mainly only doing 6 mile runs to and from work so it may not even be far enough to build up a big vacuum.
To be honest, i'm just trying everything, one thing at a time, until i figure it out.
I might try blowing air up from the bottom of the tank which will be easier to feel if it's blocked or not. I can't see why it should be though as it all looks like a sealed unit once the cap is locked down.

[fazersharp]

As a lay-man, I would think a blocked breather would cause the tank to gain a negative pressure so that when you open the filler cap a loud hiss of air rushing in would be apparent. Is that the case?

I think if it was totally blocked it would do that, but if it was that bad it would also run like shite or even cut out.
Once it's started, eventually, it appears to run okay though. I'm mainly only doing 6 mile runs to and from work so it may not even be far enough to build up a big vacuum.
To be honest, i'm just trying everything, one thing at a time, until i figure it out.
I might try blowing air up from the bottom of the tank which will be easier to feel if it's blocked or not. I can't see why it should be though as it all looks like a sealed unit once the cap is locked down.

Have you tried taking it out for a dam good thrashing

[darrsi]

As a lay-man, I would think a blocked breather would cause the tank to gain a negative pressure so that when you open the filler cap a loud hiss of air rushing in would be apparent. Is that the case?

I think if it was totally blocked it would do that, but if it was that bad it would also run like shite or even cut out.
Once it's started, eventually, it appears to run okay though. I'm mainly only doing 6 mile runs to and from work so it may not even be far enough to build up a big vacuum.
To be honest, i'm just trying everything, one thing at a time, until i figure it out.
I might try blowing air up from the bottom of the tank which will be easier to feel if it's blocked or not. I can't see why it should be though as it all looks like a sealed unit once the cap is locked down.

Have you tried taking it out for a dam good thrashing

Not sure what purpose that would serve, it's a starting issue, not a running one.

[darrsi]

The K&N air filter was cleaned not so long ago, and if you speak to my work receptionist she'll definitely confirm it's getting petrol by the way it has backfired in the past letting out a flame like a jet planes afterburner and a noise like an elephant gun.
The battery is good, that consistently supplies power when it's trying to start, without any signs of pegging out, it's just that the engine doesn't want to catch.
Quite a few times it's started for about a second or two, then just cut out, then it takes about another 2 minutes of trying to start it, with and without the choke before it will eventually catch and run as if there was never a problem.
But thinking back it's always misbehaved in hot summer or in cold winter evenings after work, which is what led me down the blocked air vent path.

[fazersharp]

As a lay-man, I would think a blocked breather would cause the tank to gain a negative pressure so that when you open the filler cap a loud hiss of air rushing in would be apparent. Is that the case?

I think if it was totally blocked it would do that, but if it was that bad it would also run like shite or even cut out.
Once it's started, eventually, it appears to run okay though. I'm mainly only doing 6 mile runs to and from work so it may not even be far enough to build up a big vacuum.
To be honest, i'm just trying everything, one thing at a time, until i figure it out.
I might try blowing air up from the bottom of the tank which will be easier to feel if it's blocked or not. I can't see why it should be though as it all looks like a sealed unit once the cap is locked down.

Have you tried taking it out for a dam good thrashing

Not sure what purpose that would serve, it's a starting issue, not a running one.

Your bike is bored with the 6 mile commute, its fed up, I promise you, give it a blast and the next time you come to start it will  going before your thumb has even touched the button.   

[His Dudeness]

Next time it happens take a plug out and check if it's sparking and what condition it's in if it's wet etc

[darrsi]

Next time it happens take a plug out and check if it's sparking and what condition it's in if it's wet etc

Can't see why it wouldn't be, as said once started it runs fine.
I chopped the ends of the HT leads and rescrewed the caps on firmly, got new Iridium plugs, and i've covered them in WD40 as well to avoid damp issues.
Don't forget, this isn't a recent issue, it's been happening since summer so i've done all the main checks and replaced a few parts along the way.
The air vent theory was only thought of when i was searching the web a few days ago, but i've got this week off work so not been doing the commute.
I was out on the bike yesterday but i'd already opened the fuel cap to blow air down the hole, plus the weather was warmer, and the bike started up fine straight away.
The main time it plays up is after it's been sitting outside work all day as i'm going home. It's played up a few times in the morning but not as bad, although it is garaged at night so that may be why.

[slappy]

Don't know if you have tried this but next time you start it up at work open the fuel cap first, then start it up. If it starts up ok then I would  check  that  all the hoses are clear of debris and gunk and not kinked and replace them. I realise that you have said before that you have  checked them but if it is mayonaise type gunk it is hard to clean it out properly and replacement hose is cheap.

[darrsi]

Don't know if you have tried this but next time you start it up at work open the fuel cap first, then start it up. If it starts up ok then I would  check  that  all the hoses are clear of debris and gunk and not kinked and replace them. I realise that you have said before that you have  checked them but if it is mayonaise type gunk it is hard to clean it out properly and replacement hose is cheap.

Think my new fuel cap is possibly due today, so if that turns up i'll sort that out for starters.
And i'm gonna use a pipe from my CarbTune kit with a can of compressed air and fix it to the metal vent nipples underneath the tank and blow air upwards and see if it comes out okay at the top.
On my bike the tank vent/overflow nipples are lowered into a rubber cup to avoid kinking issues, so the hoses that run downwards from that cup should in no way be kinked as i've never needed to displace them but i'll most certainly check if they're gunked up with anything. On earlier models they do have pipes coming off the tank which i know were prone to accidentally being kinked, if not routed correctly or pulled downwards when the tank is lowered.   

[darrsi]

So the vent and overflow pipes were all good. I pushed some air through them from the 2 metal pipes at the bottom of the tank and air flowed freely, plus the rubber hoses that run down from the rubber cup under the tank were all clear as well so no excuses there.
New cap arrived as well so that's now fitted.
On the old original cap it had a plate with a pin hole that lowered specifically on to the orange rubber housing. The rubber housing covers the breather pipe that goes straight through the tank from top to bottom, and protects it from any fuel going down it.
The replacement cap doesn't have that plate, so if anything it will now have access to even more air.
If there was any lack of venting then it will be inside the cap mechanism itself, so now i've got a shiny new one i can rule this out if it ever plays up starting again.
Won't really know now until it's sat outside work all day again, which won't be 'til next week when i go back, so i'll be back if it ever doesn't start. 

[darrsi]

For anyone who doesn't know, the lower hole is the cap breather that goes straight through and gets covered by the orange rubber cap.
And the hole to the left is the drainage hole for excess fuel, or any water that may leak through.

The rubber gasket was in very good nick so i just cleaned it up and swapped it over.