Fuel line empties when disconnect

I have a clear fuel line with clear in-line fuel filter.
I have been monitoring the fuel level in line.
I leave the petcock on RES.
I ride and then leave bike on center-stand overnight.
The next day, the fuel line will be full, virtually no air bubbles.
When I disconnect the fuel line at the petcock, the line empties the fuel into carbs.
Why?

 

1. Res is for RESERVE. This is so you don't run out of gas unexpectedly because your fuel guage flaked out or your were not watching your mileage.

2. These oem petcocks are vacuum based. So I would expect a little gas to flow thru the tubes when you disconnect it from the tank.

If it is FLOWING and totally flooding your carbs, others will have to answer your questions.

Prime on the petcock is used to "prime" a dry carburator after working on it and/or for draining your tank while its still on the bike.

ON on the petcock is the normal operating position, and the fuel should only flow while the bike is running and the vacuum system is working properly. The also acts as the "off" while disconnecting your tank for what ever reason.

 

I'm guessing what you are observing is more a vacuum thing. When the engine shuts off, the petcock should also shut off and no fuel flows into the float bowls, but there could still be a partial vacuum/void somewhere between the petcock and the bowls. Disconnecting the fuel line at the petcock brings the partial vacuum to ambient air pressure and the fuel fills the void (wherever it is). If fuel is not leaking past the petcock or the float valves with the engine shut off, I'd not worry about it.

 

straw in a coke. You put your finger over the end and lift up the straw stays full. Take your finger off coke spills everywhere.

Same thing.

 

I understand that the petcock is holding back the gas via (surface tension I think is the term) because the line is closed at the petcock end. When I slowly remove line from petcock, air is introduced at that end of line. Then the fuel in line empties into carbs.

(me thinking out loud)
So the carb bowls should have been full to proper height when I turned off the bike (Bike runs good BTW). The needle and seat on float function (seal) well enough for good running operation of the bike.

(Then I get brain freeze)
If the carb bowls are draining overnight, where are they getting the air to over-come surface tension? The bowls are not being supplied with gas – the gas is held in the line. Where is the gas draining into? How does the gas get lifted up out of the bowls?
If the gas is not draining from carb bowls overnight, they should be full, so then how does the gas from line enter the bowls when I disconnect the line?
(I know that may sound very confusing, but that is the reason I ask)

[iwingameover – I like your new avatar ! Fits well with your nickname ]

 

Your carb bowls may not be completely full when the bike gets shut off. You're also talking about a relatively small volume of gas in the line.

[Thanks. It's also on my rear fender.]

 

I agree that is a small amount of fuel. But it still leaves me wondering.
Here’s my concern. I have recently been paying (in time mostly) lots of over-due attention to my Seca. I have been taking the tank off & on, riding, tank off & on, ….
So that little bit of gas in line each time adds up.
My oil (fill hole) smells of little bit of gas. The oil is only a few hundred miles old.
I’m wondering if, and if so how, that gas is getting into crank case.
(I understand the gas in oil could be from another cause, but sometimes tracking down the cause is what life is all about !)

 

You probably have float(s) leaking. That would also explain why the oil smells like gas.

The vacuum valve on the fuel cock is a safety to prevent the tank from emptying if float valves fail.

 

+10...

Couldn't have said it better.