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Discussion Starter · #1 ·
Hey guys,

I noticed the last time I filled up that there was a definite hiss of air when I popped open the cap.

Is there a vacuum being created by a cap that seals too well... hence the rough running at low revs?

Am I on glue for thinking there might be some explanation for it?
 

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Hiss on opening gas tank

I have heard the same hiss.
 

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Mine does it too, but most cars do also. I don't think it's a problem.
 

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Discussion Starter · #4 ·
I have never noticed it on the cars... must be just me. I was remembering how a choked cap will not allow air in to displace the fuel used and sometimes it would starve a motor for fuel. I have seen it with outboards and other small motors but they have carbs too so... must be me.
 

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Bon Vivant
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Did you guys remove the evap can and plug the vent line?

If you remove the evaporator canister you need to keep the tank vent open and plug the smaller line to the cylinders.

Mine does not hiss
 

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Discussion Starter · #6 ·
Mine is bone stock. Yours didn't hiss and it still runs rough huh flynbulldog?
 

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Did you guys remove the evap can and plug the vent line?

If you remove the evaporator canister you need to keep the tank vent open and plug the smaller line to the cylinders.
I would like to do this, like I did on my Daytona 675. Is there a thread on the proper procedure?
 

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I have never noticed it on the cars... must be just me. I was remembering how a choked cap will not allow air in to displace the fuel used and sometimes it would starve a motor for fuel. I have seen it with outboards and other small motors but they have carbs too so... must be me.
My daughters 2007 Beetle does it pretty loud, and so do some of my other cars. Maybe it's a Euro 3 emissions thing.
 

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Discussion Starter · #9 ·
Hey, that would make sense and since I am old... I would not be used to such new-fangled technology! Wifey's car is a flex and has the "ultra high tech no gas cap flap door thingy" so I never hear it hissing (the car I mean).
 

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Bon Vivant
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Mine is bone stock. Yours didn't hiss and it still runs rough huh flynbulldog?
When I first removed the Evap can I plugged the wrong line and the cap hissed when I opened it.
I talked with one of the techs at a local dealer and he set me straight on how to set up the lines once the canister was removed. Now it's just like stock and doesn't hiss.
All this has nothing to do with how my bike runs...

Side note: removing the canister does not improve performance, it only absorbs raw fuel vapors to lower emissions from raw gasoline, there's really no real reason for anybody to remove it on this bike other than to unclutter the look - but in my opinion it doesn't help with that much either.
 

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Discussion Starter · #12 ·
Well, thanks for setting my straight... I am looking forward to a fix for it too. I seem to recall the old days with those rip snortin' beasts that never ran well below 4000 rpm, was it Eddie Lawsons bike? Makes me feel like I am riding a rip snortin' beast!
 

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Discussion Starter · #13 ·
Ok, I may be on glue here but, just for a laugh I opened the gas cap (I had stopped for gas and found it almost difficult to release the vacuum and open the frigging cap) and rode it around just closed, not latched and wondered to myself it it wasn't slightly smoother.
I found less popping on decel, smoother slow speed driving (1st gear is sort of wacked normally) and 2nd at slow speeds was jerking along some till I tried my experiment.
I find I can drop revs down to even 3000 and gently twist for more and it just motors up, there is still a slight surge from around 3750 to 4000 but not a spronounced to me anyway.
Please try it for me also and see if I am dreaming or there is something to it?
I am going to look into the venting and charcoal canister deal and see if there isn't something I can do to help it along and maybe the ECU re-flash will be better also?
Like I said, I might be dreaming but... try it?
 

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When I filled up yesterday, I heard no hiss but could see the reflection of vapors emanating from the tank. I don't have a flat spot issue either before or after the remap, but she definitely does not run smoothly below 3 grand. This only comes into play at left and right turns in the city where I need to downshift into first to be able to come out of the corner smoothly. The bike runs better above 4 thou and it seems to me that the real power comes on at 6
 

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Hi new to the Forum but without having intriduced myself....

Had also noticed a vacuum build up in the tank, and associated it with rough running. Ducati have told my dealer that a small number of tanks have not got a breather hole drilled somewhere around the cap fitting. I have been asked to take the bike back for this to be rectified.

Sorry don't have any precise details, other than the cap needs to be removed to fix the problem
 

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Dealer fixed the Gas cap vacuum

Ok just done 90 miles after the fix was carried out. Now the bike runs more smoothly, and is more responsive - a real pleasure - still slightly off/on in traffic, but not enough to worry about. Pulls cleanly from 2.5K -so now I'm haaaaappppppyyyy.........:D

The hole needed to be drilled in the white tank material under the cap, it coresponds to a hole in the rubber gasket, and is close to the second hole that joins on to the pipe that on UK bikes joins to a T piece and ends on the right of the sump area. There is a raised oblong section in the black plastic on the right hand side of the gas cap that you can see when filling with fuel.. ie on the underside of this there should be two holes, in the cap itself and in the tank. Mine had only one.
 

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When I first removed the Evap can I plugged the wrong line and the cap hissed when I opened it.
I talked with one of the techs at a local dealer and he set me straight on how to set up the lines once the canister was removed. Now it's just like stock and doesn't hiss.
All this has nothing to do with how my bike runs...

Side note: removing the canister does not improve performance, it only absorbs raw fuel vapors to lower emissions from raw gasoline, there's really no real reason for anybody to remove it on this bike other than to unclutter the look - but in my opinion it doesn't help with that much either.
Actually removing the canister will eliminate the vapor build up that can cause the bike to run rough and stall in high heat situations. It happened to me, that's why I removed mine.
 

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Remember the sticker on tank when you first got your bike? It warns about proper filling level, so fuel won't overflow to this damn canister and cause rough starts and idling. First thing I've done was to remove sticker, second to chuck this ugly crap device, which is there only to satisfy bureaucrats while possibly impairing bike operation.
 

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Bon Vivant
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The hole needed to be drilled in the white tank material under the cap, it coresponds to a hole in the rubber gasket, and is close to the second hole that joins on to the pipe that on UK bikes joins to a T piece and ends on the right of the sump area. There is a raised oblong section in the black plastic on the right hand side of the gas cap that you can see when filling with fuel.. ie on the underside of this there should be two holes, in the cap itself and in the tank. Mine had only one.
Do you know if this is only on UK bikes or on all SF's?
 
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