[MMRanch]

Hay folks let me ask ya'll :   

For as long as I've had my Super Meteor , when I stop to re-fuel and open the fuel cap ... it relieves pressure when I open the cap. 
Yes "Every time"

Before I go chasing a problem , I'll ask ... 
Is this NORMAL ?

I've had the tank off a time or two , but don't really like doing it !   
But
If its necessary then It's NECESSARY !   

I've got a little more than 3,350 miles on it now , I  have started ridding the 650 more often than I used to .   It does all the stuff the 350 Meteor does except the 80-85 mpg part !   
 

[MMRanch]

OK

Maybe I worded this wrong ?
.............

28 views and NO replies.

I just rode home on an empty tank (224 miles on the tank full)  .
Before I take it anywhere else I've got to get fuel.
So
While the tank is empty I'm going to pull it off to check the vent hose and such.

Please post any advice ... I'll wait until tomorrow to put it back on unless I find an Obvious problem.

[Dexter]

Normal. Happens with all vehicles now due to emission regulations, which are intended to keep fuel vapours out of the atmosphere as much as possible.

My Honda ST1100 from 1995 did this and occasionally I could hear a farting noise in the garage after a hot ride, which was the tank's pressure relief valve venting excess pressure.

[deadbat]

Quite normal I would say. I'm not an engineer, so happy to be corrected, but I would say that when you open a fuel cap the pressure inside the tank is  trying to equal the pressure outside.
In empty tank the difference will be greater than in tank that is half full, so if you regularly ride to the very last drop then you'll be more likely to hear hiss every time you open a fuel cap.

On a side note RE recommends refueling as soon as the fuel indicator starts flashing to avoid damaging the fuel pump.

[Dexter]

Quite normal I would say. I'm not an engineer, so happy to be corrected, but I would say that when you open a fuel cap the pressure inside the tank is  trying to equal the pressure outside.
In empty tank the difference will be greater than in tank that is half full, so if you regularly ride to the very last drop then you'll be more likely to hear hiss every time you open a fuel cap.

On a side note RE recommends refueling as soon as the fuel indicator starts flashing to avoid damaging the fuel pump.

This bolded statement above is exactly correct. Less fuel equals a greater quantity of fumes, which can be compressed. The fuel itself cannot be compressed. You can observe greater swelling on a plastic jerry can that is nearly empty than on one that is full, sitting sealed for the same length of time.

The engine heat causes the expansion and compression of the fumes.

[deadbat]

You can observe greater swelling on a plastic jerry can that is nearly empty than on one that is full, sitting sealed for the same length of time.

The engine heat causes the expansion and compression of the fumes.

Am I correct thinking that outside temperature can also be influential? Let's say for example I park my bike (which has almost empty tank) outside in 30°C heat. Would that also cause expansion of fumes in my almost empty tank?

[Dexter]

Am I correct thinking that outside temperature can also be influential? Let's say for example I park my bike (which has almost empty tank) outside in 30°C heat. Would that also cause expansion of fumes in my almost empty tank?

Yes. Any heat rise within the fuel tank will raise the pressure somewhat. Fuel systems are designed to vent excess pressure before any problems can arise from it though, usually through the fuel cap, or an emissions control device that captures the fumes and puts them back into the engine after running, or absorbs them into carbon. so no need to worry about it.

[deadbat]

Yes. Any heat rise within the fuel tank will raise the pressure somewhat. Fuel systems are designed to vent excess pressure before any problems can arise from it though, usually through the fuel cap, or an emissions control device that captures the fumes and puts them back into the engine after running, or absorbs them into carbon. so no need to worry about it.

That's what I thought. Thanks Dexter.

[MMRanch]

 

    So

A Light color will Fart less than a Dark color on a hot day ?   
...........

I pulled the tank and found the vent hose was clear ...
So
Then I found the tank bag that fits under the fuel cap was plugging the hole feeding the vent tube .   The excess pressure was an oversight on my part (we should have know RE could never screw anything up).

I got a good hole puncher and cut a hole in the tank-bag-lip that fits under the fuel cap.    There is only the "Normal" pressure now.   

I feel a little silly for having to pull the tank in order to find a covered vent hole under the fuel cap ...  .
I must have needed the practice getting the tank off ?

Thanks for all the replies.   

This the tank Vault its really easy to like all the compartments

https://www.ebay.com/itm/196307935470

It fits both Meteor bikes with a center fuel cap.