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View Full Version : Is vacuum pressure in the fuel tank normal?



kchan1100
04-04-2004, 03:19 AM
I notice when I refuel my bike, the gas cap is always vacuumed to the tank. I have to use my key as a handle to pull the cap till air rushes into the tank. Is that normal? It does not seem to effect the fuel system at all. Just curious. Please advise.

Thanks

Kenny

HixX
04-04-2004, 03:20 AM
Ive never had it ?

Thunder Factory
04-04-2004, 04:51 AM
Originally posted by kchan1100
I notice when I refuel my bike, the gas cap is always vacuumed to the tank. I have to use my key as a handle to pull the cap till air rushes into the tank. Is that normal? It does not seem to effect the fuel system at all. Just curious. Please advise.

Thanks

Kenny

Kenny

Have you that crazy emmissions cannister fitted?

mille-ryan
04-04-2004, 05:02 AM
Ya shoulda done a little search man, lol. We were discussing this on my non CA model last week.And yea my bastard is still holding pressure, Aprilia has not called back to help as of yet, go figure.:mad:

kchan1100
04-04-2004, 07:07 AM
ryan,

I did see your post about a pressurized tank but I read it as your bike having too much air IN your tank. My issue seems like air is unable to vent into the tank to compensate for the gas being pumped into the fuel system. Do we have the same issue? Must of read it wrong. Did you try doing what Norcal Factory suggested? And yes I do have the emissions thingy.

mille-ryan
04-04-2004, 07:41 AM
LOL, ya sounds like we have the same problem, Im sure once it gets warmer many other will too. I checked for the valve like NorCal was speeking of, and my bike doesnt have that stuff installed.

DockingPilot
04-04-2004, 08:09 AM
Kenny,
No, dont see this on mine. Intrestingly, my bike is # 0002, which means the 2nd one made. You would think I would experience all these problems listed (and I still might). However, outside of the weak rear brake, which my dealer will bleed upside down as suggested here, I have not seen any of the faults listed on this board on my ride..........again, yet anyway. Obviously, you have faulty vent line.
Ive owned many bikes, from Yamahas to BMW's, still do, but I love this bike, it's a keeper ;)

Dvus
04-04-2004, 08:35 AM
could be that one of the breather tubes is being pinched. I noticed it on mine when I had that problem. I lifted the tank and looked at the tubes when I lowered it and when it got close to being all the way down, I noticed that one of them was bent where it wasn't functional any more. So what I did was to zip tie it to where it wouldn't bend when I lowered the gas tank. That solved my problem. I don't know if that would be the same problem you are experiencing but well worth looking into. Good luck.

clarkie49
04-04-2004, 09:17 AM
get rid of the event tubes altogether, one way to check if it fixes the problem, and does anyone really care about the 'legal' side of the emmissions once they own the bike?

for instance, removing the Cat from your exhausts is a federal offence, but no one cares about that so why worry about the tank vent lines :D

Dvus
04-04-2004, 10:04 AM
I wouldn't want to remove my vent tubes. I notice after I run the bike, there are some small puddles of fuel coming from the tubes. I wouldn't want any of the fuel drip on the engine especially after riding in the summer heat.

kchan1100
04-04-2004, 05:30 PM
I wouldn't mind removeing my emissions system. Just need to know how and what to remove. I checked all my vent lines yesterday and could not find anything pinched. I did find this image from an old post. Correct me if I'm wrong but the fuel tank breather line (3) is connected to a 2 way ventilation valve. I thought that was suppose to be a one way valve? If indeed it is a 2 way valve, can I just bypass it? ie. remove the valve and replace it with an open valve. What is a 2 way valve and how is it different than an open valve?

Thanks

Kenny

clarkie49
04-04-2004, 06:18 PM
Originally posted by Dvus
I wouldn't want to remove my vent tubes. I notice after I run the bike, there are some small puddles of fuel coming from the tubes. I wouldn't want any of the fuel drip on the engine especially after riding in the summer heat.

if there is fuel coming from the tubes (even a small amount) you have a problem.

one is a breather and the other is the overflow for when you overfill your tank

kchan1100
04-04-2004, 06:46 PM
I just removed the valve on the fuel tank breather line and it is only one way with the flow going away from the canister and into the fuel tank. I removed the valve completly and tried to blow air into the fuel tank, with the cap opened of course, but couldn't. Is that right? How is the fuel tank suppose to vent air? Please advise. Clarkie???

msv
04-04-2004, 07:09 PM
I just picked up my RSV on Friday :) I'm planning on removing all of the evap emissions stuff shown in that diagram, putting a cap on the vacuum port at the throttle body and routing a hose from the tank vent to a safe position. I haven't had it apart yet, but if I've read the hose routing correctly, the other vacuum line that comes off the tee right before the throttle body is for the flapper valve actuator, so this will serve to disable that as well.

Mark

skykasl
04-04-2004, 09:15 PM
I just removed the valve on the fuel tank breather line and it is only one way with the flow going away from the canister and into the fuel tank. I removed the valve completly and tried to blow air into the fuel tank, with the cap opened of course, but couldn't. Is that right? How is the fuel tank suppose to vent air? Please advise. Clarkie???

Hey kchan100,

I removed the canister in the rear and connected all the vent lines together using a 3 port tee. System still vents w/o any problems. PM me and you can shoot by for a look if ya want.

John

vtrandall
04-04-2004, 09:27 PM
Originally posted by skykasl


I removed the canister in the rear and connected all the vent lines together using a 3 port tee. System still vents w/o any problems. John

that's a cool idea....and simple !!

randall

msv
04-04-2004, 09:53 PM
Originally posted by skykasl
I just removed the valve on the fuel tank breather line and it is only one way with the flow going away from the canister and into the fuel tank. I removed the valve completly and tried to blow air into the fuel tank, with the cap opened of course, but couldn't. Is that right? How is the fuel tank suppose to vent air? Please advise. Clarkie???

If you look at the diagram above, it shows the check valve in the vent line oriented to allow flow away from the fuel tank, so yours was (is?) in backwards it would seem.

zxrcy
04-05-2004, 12:08 AM
Originally posted by clarkie49
if there is fuel coming from the tubes (even a small amount) you have a problem.

one is a breather and the other is the overflow for when you overfill your tank


What might cause this puddle. I have a Canadian bike (no canister) and I get drips of gas coming from the vent line after a ride ???

kchan1100
04-05-2004, 04:28 AM
With the use of my mity vac, I was able to test both the overflow hose and vent hose. First I opened my fuel cap. When I connected the vac to the overflow hose I was able to hear the air sucking from the hole under the fuel cap. That appears to be working fine. I then removed the 1 way valve completely and connected the vac to the vent hose. Started pumping and nothing was happening. I was able to generate a good suction but it was not relieving inside the tank. Then I connected a small compressor to the vent hose and pumped air into the tank. That also did not relieving inside the tank. Could the venting system in the tank be faulty? Is there a valve inside the tank that only works when there is a certain amout pressure? Shouldn't the vent be free flowing like the overflow? Please advise.

If it's not too much to ask, could someone, not having this issue check if their vent hose is free flowing? The one way valve is located on the right side below the rider's seat. If you remove the plastic/carbon fibre panel, R/Factory model, under the seat, the valve is out in the open. Remove the valve completely and check to see if you can blow air into your fuel tank freely, with the fuel cap opened of course.

Thanks

Kenny

Thanks

mille-ryan
04-05-2004, 04:37 AM
Just one more thing, make sur ethat your dealer puts in a claim or concern to Aprilia, so they have to adress and fix it. Its the only way to get it done right, and make the futre bikes better.

kchan1100
04-05-2004, 12:48 PM
bump

zxrcy
04-05-2004, 04:35 PM
Can anyone post the schematics for a non California bike, my shop manuals have not come in yet. Canadian bikes have no canister and only one check valve in the vacuum line. The overflow & vent lines come out of the bottom of the tank and are routed to the bottom of the bike & out the hole in the fairing. When I tipped the full tank up the dripping out of the one hose increased until I pulled off the vacuum line check valve. It seemed to stop at the same time. The vacuum check valve seemed to take a fair bit of pressure to actuate. Anyone understand how this system works & why it would drip gas after running the bike?

kchan1100
04-05-2004, 05:16 PM
Left a message with Aprilia USA tech support and got a call back within 30mins. Told the tech about my vacuum issue and apparently my tank is faulty. The tech was great. I told him that I removed the one way valve and tried to blow air into the tank but was unable to. The tech then went to a bike they had there and did the same thing (now that's support) and was able to blow air into the vent tube without effort. He then told me to contact my dealer and have them order a new tank for me. WHAT SERVICE!!:plus:

BTW. Here's a piece of important info. The tech also told me that the 1 way valve is actually a 2 way valve. The black end SHOULD be connected to the canister side and the grey end connects to the fuel tank side. Here's how the 2 way valve works. Air is suppose to flow freely from the canister to the tank. If you remove the valve, you can blow air into the black end easily. Fuel vapors are suppose to flow from the tank to the canister. The valve WILL open at a certain psi allowing flow from the grey end to the black. If you try to blow on the grey end, it won't work cause you need to generate a certain amount of psi before it opens. Just an important FYI.

Gonna call my dealer tomorrow and order my new tank.:D

kchan1100
04-05-2004, 05:23 PM
Originally posted by zxrcy
Can anyone post the schematics for a non California bike, my shop manuals have not come in yet. Canadian bikes have no canister and only one check valve in the vacuum line. The overflow & vent lines come out of the bottom of the tank and are routed to the bottom of the bike & out the hole in the fairing. When I tipped the full tank up the dripping out of the one hose increased until I pulled off the vacuum line check valve. It seemed to stop at the same time. The vacuum check valve seemed to take a fair bit of pressure to actuate. Anyone understand how this system works & why it would drip gas after running the bike?

How is the valve connected to the vent hose? Is the grey side connected to the fuel tank end?

zxrcy
04-05-2004, 07:13 PM
There is no valve in the vent line- I traced it to the end. There are two lines of the same size that come off the bottom of the tank and lead down to the bottom of the fairing. I presume one is a vent line and one is the overflow that comes from the filler ring. The valve is in a secondary fatter hose that comes from the bottom of the tank leads under the intake from the left side comes out on the right side has a check valve in it and leads into the intake throttle body. The valve free flows towards the throttle body.
When I run the engine it slow drips a bit of gas after shutoff for a few moments, then stops??????

mille-ryan
04-05-2004, 07:31 PM
Hey why dont somone post a real life pic of this check vlve and where its located on the bike. Teal pics are soo much easier to desifer than diagrams.

clarkie49
04-05-2004, 10:29 PM
Originally posted by kchan1100
The valve WILL open at a certain psi allowing flow from the grey end to the black. If you try to blow on the grey end, it won't work cause you need to generate a certain amount of psi before it opens.


that is a lot of pressure :rolleyes:

Norcal Factory
04-16-2004, 04:26 PM
Mine makes a high pitch squeling noise after riding with the tank 1/2 full or less. You can hear it after stopping the engine. If you lift the tank cap it all escapes with a hiss.

Time to remove the "1 way valve" and plug the vacum lines at the manifold or at least connect them together as mentioned earlier in this thread.

417RSV
04-16-2004, 05:42 PM
Kchan...

I have the same problem on my R model. Especially if it's at the end of a long ride and the bike is on vapors, the tank has a HUGE vacuum. Gotta let the pressure equalize or else the vacuum rush explodes the remaining fuel all over the place.

kchan1100
04-16-2004, 05:47 PM
Dude,

I got the fix for ya. PM me your number and I'll give you a call.

Norcal Factory
04-17-2004, 11:13 AM
I removed the canister in the rear and connected all the vent lines together using a 3 port tee. System still vents w/o any problems. PM me and you can shoot by for a look if ya want.



I wouldn't reccomend this. If you do it, you essentially have a vacuum leak. See the diagrams in earlier posts.

The symptom will be a slight bog at around 6,250-6,500 PRM. You will get the same symptom if you just disconnect the carbon canister without capping the vacuum lines.

Just buy a 1/4" plug for the fitting on the throttle body where the vacuum line attaches. It's on the right side under the tank- no need to take off the fairings.

Now you will be able to remove the carbon canister (CA models), the "1-way valve" from the tank pressure relieve tube, and if you want, the flapper tubing.

Your flapper will be stuck in the open position allowing more air in (and noise out) at RPMs below 6,500.

vtrandall
04-17-2004, 12:00 PM
I removed the carbon can from my Superhawk and just let the lines vent to air with out any problems...but the VTR is carburated compared to the Mille and I don't think there are any one valves either....hmmmm....

randall