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Discussion Starter #1
Was actually picking up the new coils when this happened.

For some strange reason, it started to seep a bit of fuel through the fuel cap keyhole. After i shut the bike i can hear it weeping from the keyhole, and while doing that, it bubbles a tad of fuel, not much but just making the keyhole surrounding moist.


Can a fuel cap really go bad? Im a bit lost here ?? :nerd2:
 

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Hi Viggen, it would be very helpful if you included the model / year in your post (your name suggests an F4...but that's about it). Some details on the bike such as vintage, kms, history etc.

apologies - I see you've just posted about the Coil in an earlier thread.


Cheers
 

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The gas cap vent is blocked causing pressure inside to seek another path...... Check the vent hose from the bottom of the tank. Also check the little rubber seal between the cap and the tank.

Do you still have the evaporative emissions system in place? That would add to the diagnostic steps.
 

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Discussion Starter #5
Esq.

The hose looks fine by eye, and no kinks. So maybe it could be something blocked inside the cap itself, have to take it apart. The bike had been sitting for very long time before me, so it is possible that something inside the cap is clogged up! It has no emission gear in place.

Edward.

The cap itself does not leak, its the pressure build up that comes through the keyhole. I always leave a litre or so down from full tank, alltough i always filled my previous F4 1000 to the brim, and it never leaked.
 

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On the side, you may find deteriorated fuel line hoses in your tank. I know that may not explain the keyhole weeping but it if your bike sat for a while with gas in the tank that may be the underlying issue.
 

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The pressure vents through a labyrinth in the cap to a hole to the side, connecting between the cap and tank by a small mushroom shaped rubber seal that leads to the hose out the bottom of the tank.

Look at the seal when the cap is open and blow some air through it to confirm passage is clear. Unusual for the labyrinth in the cap to become blocked.
 

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Discussion Starter #11
Take the fuel cap apart, there is an O-ring at the bottom of the lock tube, thats leaking.

Use a proper green one, the OEM black will perish once it touches ethanol.
 

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?

Take the fuel cap apart, there is an O-ring at the bottom of the lock tube, thats leaking.

Use a proper green one, the OEM black will perish once it touches ethanol.
Wrong!!!!!
You want a Buna-N O-rings which just happen to be the recommended material for gasoline AND Ethanol......look it up in the compatibility chart

The whole green O-ring thing was started by Ducati......so they could sell a $0.30 O-ring for the fuel pump plate for $17>:)

I use the aftermarket caps without any check valves and plug the vent hole in the tank behind the cap>:)

This is all that's inside my fuel tank besides the fuel pump plate assembly, it's a stock MV part #800095839
(hose clamps are added at installation)
 

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Discussion Starter #13
My black one was resembling liquorice, but you are right about the O-rings.

Changing a cap was also on my agenda, but you cant use a cap without lock here.
 
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