Fuel bubling through keyhole - MVAgusta.net
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post #1 of 13 (permalink) Old 05-15-2019, 10:04 PM Thread Starter
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Fuel bubling through keyhole

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 ??
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post #2 of 13 (permalink) Old 05-15-2019, 10:31 PM
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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.


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post #3 of 13 (permalink) Old 05-16-2019, 05:57 AM
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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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'08 910R (Gina), '04 F4 SPR #275 Track Bike (Lola), YSR50 (The Rabbit), '71 CB100 (Lil' Red), '75 RD350C (Orange Bird) restoration project, '08 TT-R110 (Buster) Pam's ride, 2015 Indian Chieftain (Rita) my "low-n-slow", '70 Suzuki F50 (Baby Blue), 2018 Suzuki GSX-S750L8 (Susie Q)
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post #4 of 13 (permalink) Old 05-16-2019, 06:37 AM
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and more obviously not to overfill your tank. --especially with any possible blocked vents or leaking cap gaskets.

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post #5 of 13 (permalink) Old 05-16-2019, 07:02 AM Thread Starter
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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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post #6 of 13 (permalink) Old 05-16-2019, 07:13 AM
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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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post #7 of 13 (permalink) Old 05-16-2019, 07:39 AM Thread Starter
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Hoses are new. And if they`d pop, the gas would leak from the overflow to the ground.
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post #8 of 13 (permalink) Old 05-16-2019, 09:09 AM
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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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post #9 of 13 (permalink) Old 05-16-2019, 12:48 PM Thread Starter
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O-ring was bad at the bottom of the lock tube. Sorted now i believe, alltough did not have time for a test ride.
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post #10 of 13 (permalink) Old 05-22-2019, 05:58 AM
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Quote:
Originally Posted by ViggenF4 View Post
O-ring was bad at the bottom of the lock tube. Sorted now i believe, alltough did not have time for a test ride.
Iíve actually been having this same problem, what O-ring are you referring to? I have brand new fuel lines as well.
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