High fuel tank pressure

do the new shape RSVR have a tank vent as well as the over flow pipe. just got back from a ride today which had a shocking surprise in it. been riding in the heat this afternoon, when the fuel light came on a little earlier than normal. thought nothing of it and pulled into the next available petrol station. riding friend pulls along side me as i pull up to the pump and we both switch off. key in the filler cap and get an enormous blast of petrol vapor straight in the face. forced the cap shut with my fingers and had to release the pressure slowly. huge vapor cloud and almost impossible to breath. took ages for the pressure to drop off. has anyone else had this. filled up rode the 30 miles home checked the tank no pressure build up. don't know if its a blocked vent (if they have one), low fuel level on a hot day with heat from the engine just built up excessive pressure, or the fuel pump is recycling and building up high pressure. any ideas would be great fully received.

i had the same thing the other day not quite as bad just a big hiss when i opened the cap.

Been to the coast today in high temperatures, fan on every time I was at lights and nothing like that happened. The pipe for venting is near the fuel pump, I've attached a picture to show which pipe (4). Be worth checking that's not blocked or kinked on it's run.

i used to get that all the time on my RS50, my m8s were childishly obsessed with the hiss it made, haven't had it happen once on the mille tho and more than a few times its been left in the hot sun then ridden hard all the way through rush hour, crazy high engine temperatures (well 105 C seems bonkers to me..) and not so much as a little psst when i opened it to give her a drink of petrol.

Like Dave said you want to check that breather pipe isn't getting crushed, it would have to be crushed pretty bad to allow that much pressure build up surely :confused

look on the bright side though, at least you weren't smoking :biggrin

Wolf said:

look on the bright side though, at least you weren't smoking :biggrin

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Feltch me that would of been a lil surprise

little suprise wasn't in it.
i have a big ask. i wonder if someone would check their tank vent for me. if anyone has a late RSVR there are three vents which hang down under the bike accessed from the left hand side. the two larger pipes are the ones i am interested in. one is the rain vent from the filler moat. drains rain water away and any overfilled fuel. if you blow the end of this pipe you will feel the air blowing out of the small hole next to the filling hole. mine is fully clear.
the other goes into the tank, if you blow on this pipe with the filler cap open you can see fuel vapour comming out of the tank. once you know wich pipe is which, could you shut the filler cap blow up the vent hose to gently pressure the tank, and then see how it vents.
mine is definatly harder to blow up the vent line, and when i stop blowing it does vent the pressure but very slowly. you can just hear a gentle hiss. if you then pop the filler cap you do get a release of preesure.
i basically wont to know if anyone else finds that the vent feels harder to blow up than the rain drain pipe, and when it vents after you put a gentle possitive pressure on the tank by blowing up the vent with the cap shut. is it slow to vent or does it seem to vent the pressure quite quickly.
many thanks to anyone on here that is kind enough to help in this investigation.:thumbup

Thankfully no-one saw me!!

heroblob said:

i have a big ask.

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Anyone that knows me knows I think the world of my bike but they would have wondered seeing me on the floor giving the bike a blow-job!!

HB, to answer your question, mines an '07. It's reasonably hard to blow up the pipe in question and on stopping I could immediately hear the air coming back out in a controlled manner rather than one big rush. On opening the filler cap I could hear the pressure release. I would say mine did the same as yours from how you describe yours.

Hope that helps mate :thumbup

many thanks DAVERSV, i appriciate your help. i susspect there is a restictor in the vent system, if yours acts in the same way as mine. it may be worth noting that on very warm days, when the tank is low, the pressure in the tank may not vent fast enough and may result in the situation i had last week. popped out to burnham tearoom yesterday afternoon and appeard ok,
thanks again for your help.:thumbup

Thanks for the posts. Very useful info. I just bought an 08 yesterday. Rode home and filled up. Blew petrol everywhere. I sent a very "nice" email to Aprilia about it. Do you know of any fixes that have been made? I will check the pipes today to see if they are blocked or at least the same as yours and Dave's.

The unleaded only sizing fitment in the filler neck can make filling them a bit precarious. I would imagine that you stuffed the nozzle too far in and didn't leave enough gap for the escaping air to get out as the fuel went in.

I can't help with your problem but do you all sit on the bike whilst 'filling it with fuel'? Thats the impression i'm getting from the posts.

I also used to do this but stopped after talking (not bike related) to a chap with a badly scarred neck. I asked how it happened and he told me about his motorbike setting on fire!!!

He was sat astride his bike 'filling up' in the petrol station and spilled some fuel over the tank, something ignited it and the vapour from the spillage was trapped in his clothing. He was badly burned from his knees to his face as his clothing melted onto his body in the inferno. I have NEVER sat on the bike whilst fuelling up since that day, his body is really badly scarred but he made a full physical recovery after a few months in hospital.

Just be carefull chaps, it might be a million to one chance but why take the risk to squeeze an extra 1/4 litre in there?

Seems quite common, pull off the hose on the clutch side of the two hoses that are on the underside of the tank on throttle side, you need to poke a bit of fine wire in there and fit a bit of pipe to it so you can blow through it to clear it, this has happened to both my 04+ bikes

scotsy said:

I can't help with your problem but do you all sit on the bike whilst 'filling it with fuel'? Thats the impression i'm getting from the posts.

I also used to do this but stopped after talking (not bike related) to a chap with a badly scarred neck. I asked how it happened and he told me about his motorbike setting on fire!!!

He was sat astride his bike 'filling up' in the petrol station and spilled some fuel over the tank, something ignited it and the vapour from the spillage was trapped in his clothing. He was badly burned from his knees to his face as his clothing melted onto his body in the inferno. I have NEVER sat on the bike whilst fuelling up since that day, his body is really badly scarred but he made a full physical recovery after a few months in hospital.

Just be carefull chaps, it might be a million to one chance but why take the risk to squeeze an extra 1/4 litre in there?

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I dont sit on the bike when filling...and reading that post i never will

never had a problem with high pressure but it certainly sounds like a blocked/trapped breather pipe to me...