New guy here with another question. When the bike sits what should the petcock be set to since there's no Off setting?

Thanks.

It is counter-intuitive at first... but always leave the petcock in the 'ON' position.  The petcock is vacuum operated so fuel flow will stop when the bike shuts off.  Obviously use Reserve when you start to run out of fuel.  That is vacuum operated as well.  Prime bypasses the vacuum.  The purpose of prime is to allow fuel to fill the carb bowls after the bike has been sitting for some time, draining the carb bowls, or after any maintenance you need to refill the carb bowls.


If you were to leave the bike in Prime, it is possible for your fuel to overflow if your floats aren't set correctly, or your needle valves aren't seating well enough.  Normally, both the floats and needles should be fine and leaving it prime won't hurt anything... but due to this possibility, it is good practice just to leave the petcock in the on position to avoid it period.

- Bboy

Great. Thanks, Bboy.

Quote from: BockinBboy on March 05, 2013, 06:55:16 AM



If you were to leave the bike in Prime, it is possible for your fuel to overflow if your floats aren't set correctly, or your needle valves aren't seating well enough.  Normally, both the floats and needles should be fine and leaving it prime won't hurt anything... but due to this possibility, it is good practice just to leave the petcock in the on position to avoid it period.

- Bboy

Reading this, could leaving it on prime over night be used to diagnose carb problems?

In a round about way.. I guess... lol 

But I wouldn't recommend it.  If your fuel does overflow the carbs, it can fill your airbox, and get into your cylinders.  Once gas gets into the oil, you need to change the oil.  As the new mixture will not adequately lubricate the engine, which can be catastrophic for a GS...

Oh, and you are left with a low/empty fuel tank.

- Bboy

http://wiki.gstwins.com/index.php?n=Upgrades.Petcock

Read this.  It should answer your question.  Vacuum petcocks work fine.  If they overflow, it's because your needle seats are dirty or weak.

I guess I should note that the better alternative, which would effectively tell you the same thing as overflowed carbs left in prime...

Use the U-bend method to check float height.  Attach a clear hose to the carb bowl, bend the tube upward (in a 'U' shape), set the petcock to prime, and open the drain screw.  The gas that fills the tube should be level with the gasket surface of the carb bowl.  If too high, then you have an overfilling issue either cause by the floats set too high, or a needle valve issue.  If too low, then floats are set too low.  There could be other things related to this, but those are the most likely.

- Bboy

Quote from: BockinBboy on March 05, 2013, 07:35:49 AM
I guess I should note that the better alternative, which would effectively tell you the same thing as overflowed carbs left in prime...

Use the U-bend method to check float height.  Attach a clear hose to the carb bowl, bend the tube upward (in a 'U' shape), set the petcock to prime, and open the drain screw.  The gas that fills the tube should be level with the gasket surface of the carb bowl.  If too high, then you have an overfilling issue either cause by the floats set too high, or a needle valve issue.  If too low, then floats are set too low.  There could be other things related to this, but those are the most likely.

- Bboy

Thanks for the tip. mine is fine I'm just wondered for down the road when i may have this type of problem.