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DB5 fuel tank vacuum

 
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cyriel12



Joined: 30 Apr 2018
Posts: 7

PostPosted: Mon Apr 30, 2018 1:42 pm    Post subject: DB5 fuel tank vacuum Reply with quote

DB5 fuel tank vacuum problem

Maybe someone can help me here. I have a fuel tank problem on my DB5. Both hoses are free, but when i blow compressed air on the hose that goes to the right side of the filler cap i can feel whith my hand that the complete fuel filler cap comes up. I think there is something wrong with the gasket/channel. I have take the filler cap apart. There is only one opening where the hose in mounted. Do they forgot in the factory to drill a hole in the fuel tank?
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cyriel12



Joined: 30 Apr 2018
Posts: 7

PostPosted: Mon Apr 30, 2018 1:48 pm    Post subject: Reply with quote

https://i.ebayimg.com/00/s/MTAyNFg3Njg=/z/KagAAOSw-tFa5xAa/$_86.JPG
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2bims



Joined: 03 Apr 2010
Posts: 5338

PostPosted: Tue May 01, 2018 5:49 pm    Post subject: Reply with quote

The fuel filler cap is an item still used today on Modern Ducatis.....Do you actually have a problem with the bike? Why have you taken the cap off??

Even on Ducatis they use the petrol cap in different ways.....there is usually a drain hole outside the rim of the filler hole....to take away rain, water, etc into a drain hole that runs inside the tank via a pipe to a nipple in the tank to then run outside and away...to stop water contaminating the fuel.....Bike is fuel injected to a pressured tank....sometimes they have a blow off hole to relieve pressure when fuel is running out...but it only works at a certain pressure...which is why the petrol cap can still go Chhhhhhhhhhh....like opening a can of Coke.....when you release it after a hot days riding...
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cyriel12



Joined: 30 Apr 2018
Posts: 7

PostPosted: Wed May 02, 2018 7:40 am    Post subject: Reply with quote

The drain hole (left side) works fine. I`m talking about the other hole on the right side of the fuel cap.

The fueltank deforms while driving. The CHHHH... sound i have every mile when i open the fuelcap. And the engine misfires.

See this pic. I want to know why the hole in the gasket lead to nowhere:
https://i.ebayimg.com/00/s/MTAyNFg3Njg=/z/KagAAOSw-tFa5xAa/$_86.JPG
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2bims



Joined: 03 Apr 2010
Posts: 5338

PostPosted: Wed May 02, 2018 9:15 am    Post subject: Reply with quote

What is the mileage on the Bike?.....How long has it had this problem?

Bimota use "off the shelf" standard items for suppliers that supply to other manufacturers, like Ducati...which use the same petrol cap....it is not ALWAYS the case that Bimota use the same holes, or electrical connecters....it is quite often that some items have holes or connecters but are not used.....I can see two other holes in the rubber membrane....are they both "clear"....one should be the drain hole for water and the other should be the vent for the tank to allow fuel flow without causing a vaccum....use fine wire to poke the holes....

You could...as a temporary measure/check....remove the rubber ring that is in the petrol cap itself....the part you have removed....this will remove the seal between the cap and the tank....keep the fuel level low...half full or less and ride and run the bike and see if it does not deform or stop due to there being a vaccum.....this seal in the cap is to stop fuel running out over the tank when riding and cornering, accelerating and braking as the fuel will move around...so take it steady....if all is OK....then yes...it would point to the air escape being blocked.....can you remove the rubber base plate and photo to show what is beneath it?....I wouldn't at this moment "drill" a new hole in the tank where that not used hole is in the rubber membrane....manufacturers make items with multiple holes so that they can be used on different tanks with different caps and uses etc etc...
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LacsapNL



Joined: 29 Jan 2018
Posts: 2

PostPosted: Wed May 02, 2018 4:49 pm    Post subject: Reply with quote

I happen to have two tanks one has the hole in it and the other one doesn't. The one with the hole is a newer tank. The previous owner probably had similar problems and cut the rubber gasket to vent the tank.
I would advice against that because it destroyed the paint on my freshly painted tank. Gas just flows underneath.

I can't seem to find this ZADI PL575 gasket so i ordered some NBR rubber and am trying to make my own. I will then seal the rubber with some 3M 1k-pu sealant.
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cyriel12



Joined: 30 Apr 2018
Posts: 7

PostPosted: Thu May 03, 2018 6:41 am    Post subject: Reply with quote

Thanks 2bims and LacsapNL!

What is the reason why you not drill the hole LacsapNL? destroyed the paint unterneath the petrol cap?
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2bims



Joined: 03 Apr 2010
Posts: 5338

PostPosted: Thu May 03, 2018 6:51 am    Post subject: Reply with quote

cyriel12 wrote:
Thanks 2bims and LacsapNL!

What is the reason why you not drill the hole LacsapNL? destroyed the paint unterneath the petrol cap?


Because when you ride the bike....petrol will leak out due to its motion riding the bike...cornering, braking, accelerating...it moves around....unless you fit petrol foam in the tank....this will run out and over your tank and down your frame, airbox and engine and onto HOT exhaust headers etc etc....and strip paint or even catch fire.....

I'll ask again.....Whats the mileage on the bike?...if someone has owned the bike before and done some miles on it then previously not a problem...thus maybe one of the other holes that is the breather is blocked.....and this is what needs unblocking....

Ducati Monsters, scramblers, multistradas and panigales all use the same petrol cap as the Db5....thus for spares like the rubber membrane they should stock the item or be able to order one
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cyriel12



Joined: 30 Apr 2018
Posts: 7

PostPosted: Thu May 03, 2018 9:16 am    Post subject: Reply with quote

The bike has run 3000km by the previous owner and then stand in a depot for 6 years.

Driving like this is no option. The engine runs not good.

The fuel can not come out 2bims. There is a system of 2 valves and a spring in the filler cap.

I will give it another explain:
Air runs through the hose to the nipple on the fuel tank. Another hose goes from the nipple inside the fuel tank to the filler cap. Then comes the system of 2 valves and a spring (inside the filler cap) Then the air goes out the filler cap throuch the gasket at it blocks against the fuel tank (where i think the factory forgot to drill the hole)
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2bims



Joined: 03 Apr 2010
Posts: 5338

PostPosted: Thu May 03, 2018 3:07 pm    Post subject: Reply with quote

I looked today at a Ducati 1299 V4 panigale new bike...it has the same filler cap....BUT.....where the vent hole is in the rubber diaphragm there is a hole in the tank....AND....there is a hole in the filler cap also......so that any vapour can vent through the filler cap....allowing air and gases out but not fuel...

This is my fuel cap on my DB5R....as if you are sat on the bike....the hole at 9 o'clock is indeed a hole....it goes down to a nipple inside the tank on the underside of the top of the tank...and then to a hose....this is a drain hole for overspill of fuel or rain water...and would run to a hose on the bottom of the tank....I cannot see a natural "vent" for gases......Is your cap and surround the same? THe underside of my cap does not have the breather hole on the base or the cap like Ducati models have.....I would need to see pictures of the underside of the cap and the base that sits on top of the rubber membrane base plate...

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2bims



Joined: 03 Apr 2010
Posts: 5338

PostPosted: Thu May 03, 2018 3:13 pm    Post subject: Reply with quote

Looking at your picture...if it is taken from sitting on the bike...the hole at 9 o/clock is a drain hole for overfill of fuel and rain...and the hole at 3 o'clock is the breather hole....check and make sure this is not blocked...and that the square plastic block that sits on it (also at 3 o'clock) is not blocked.....prod it with a pin or blow air through it.....I would ignore the rubber membrane that has no hole in the tank beneath it...I am fairly convinced that you have a blocked breather hole at 3 o'clock either in the tank or within the filler cap plastic base unit....
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