Fuel vapors...

[RUN666]

Every time I open the aluminum Monza cap, it's under pressure and the fuel comes out as vapor...

It's very hot here and my bike is in direct sunlight, and when I stop, I get this phenomenon every time.

So Triumph designed a black plastic vented cap and a sealed aluminum cap, and that prevents the former from venting? That's strange, to say the least, right? Or maybe I have a problem...

 

[Einar]

That sounds backwards. On mine, the aluminum cap is decorative and not sealed, so nothing happens when it's opened. The black locking plastic cap beneath it is the one that's sealed.

 

[dd14x]

That sounds backwards. On mine, the aluminum cap is decorative and not sealed, so nothing happens when it's opened. The black locking plastic cap beneath it is the one that's sealed.

Ditto - the aluminum cap (on a hinge) occasionally opens up when I'm riding too - so definitely not sealed.

 

[Protonhound]

Hmm, mine vents when opening the aluminum cap. It seems that releasing it allows the actual plastic cap to do it's venting, the aluminum cap is not sealed so it's not retaining any pressure by itself. I remember a thread talking about not laying the fuel cap upside down when fueling as this sometimes will prevent the venting mechanism to work right. I read that before I even got my '23R so when I fuel up I always put the cap right side up on a piece of paper towel.

 

[RUN666]

It's good, I solved the problem thanks to a member of a French forum... When I removed the canister system, I pinched the tank's air vent when reassembling it, which explains the high pressure in the tank in the sun. The problem will be solved tomorrow!

That being said, notice that you have, under the "Monza" cap, a small moving part with a spring that presses on the plastic cap and which apparently serves to maintain the pressure on this plastic cap. I think that, when I open the "Monza" it is actually the gases blocked by the plastic cap that escape!

 

[Einar]

It's good, I solved the problem thanks to a member of a French forum... When I removed the canister system, I pinched the tank's air vent when reassembling it, which explains the high pressure in the tank in the sun. The problem will be solved tomorrow!

That being said, notice that you have, under the "Monza" cap, a small moving part with a spring that presses on the plastic cap and which apparently serves to maintain the pressure on this plastic cap. I think that, when I open the "Monza" it is actually the gases blocked by the plastic cap that escape!

Yeah, I was thinking about that spring. Are you closing the plastic cap fully to one click? I'm wondering if some of them are faulty and not sealing properly unless pressed down (such as by that spring).

I'm going to have to look more closely at my vent hose to see if it's pinched. I still get the "pressurized tank" issue despite the dealer saying they couldn't find any kinks.

 

[Protonhound]

Yeah, I was thinking about that spring. Are you closing the plastic cap fully to one click? I'm wondering if some of them are faulty and not sealing properly unless pressed down (such as by that spring).

I'm going to have to look more closely at my vent hose to see if it's pinched. I still get the "pressurized tank" issue despite the dealer saying they couldn't find any kinks.

If you've been laying the cap upside down when fueling it may be stuck as happened to others here. There is a thread about this somewhere.

 

[RUN666]

Yeah, I was thinking about that spring. Are you closing the plastic cap fully to one click? I'm wondering if some of them are faulty and not sealing properly unless pressed down (such as by that spring).

I'm going to have to look more closely at my vent hose to see if it's pinched. I still get the "pressurized tank" issue despite the dealer saying they couldn't find any kinks.

I always apply "rule number one" in this case: "never really believe what your dealer tells you...especially when he can't find the problem with your bike..."

 

[RUN666]

Well, that's it! I've just partially disassembled the tank to check the breather hose!

Apparently Triumph has reinvented the wheel again... there's a mess under the tank that even a dog wouldn't find its puppies.
Hose, two valves, a restrictor, (numbers 35, 36, 37, 38, 39) in short, I put everything back together but I really wanted to throw all this mess in the trash... Let's hope now that the tank stops emptying from the top!

 

[Einar]

If you've been laying the cap upside down when fueling it may be stuck as happened to others here. There is a thread about this somewhere.

Possible in some cases. But the purpose of the vacuum relief valve in the cap is to allow air into the tank, while preventing fuel vapors from leaving the tank. If it's stuck open, there would be no pressure differential. If it's stuck closed, the observed issue would be the tank sucking in air when the cap is removed due to a low-pressure condition. In my case, the tank expels air/fumes suddenly, which indicates a high-pressure condition and a restriction in the evap system.