Float valves and the Petcock Valve

[bryanwescoe]

The other day i noticed a dead spot of grass under my bike.  So I uncovered it and noticed that all the gas had drained out.  Upon examining the tank/carbs i found that there seems to be some leakage around the right side float bowl.  It did not look significant enough to  cause a half tank of gas to drain out (bone dry).  The whole time I believe the petcock valve was on ON but since I was fiddling with it to figure out the leak. 

After searching here, i figured out that ON on the petcock means that its vacuum fed and that PRI means its gravity fed and RES is obviously reserve (right?).  I also found something on people having issues with leaving the petcock on PRI and having the float bowls stick open.  I assume this would have caused the fuel issue. 

Can anybody give me a quick rundown of the petcock positions and any signals that mine may be malfunctioning?  Also, can someone more clearly explain the stuck float bowl situation?

How should i go about troubleshooting this?

Thanks guys.

[Jenya]

As you figured out already, ON is vacuum controlled. And so is RES. When the engine spins, the vaccum from the carb is pulling on the rubber diaphragm and opens the passage for the fuel to flow when in ON or RES position. PRI bypasses the diaphragm and allows for the fule to flow into carbs all the time. If floats get stuck or needle jet doesn't close the hole in a carb properly, the whole tank of gas will drain, most likely via air box.

Now, if you are certain that petcock was on ON position at the time of incident, and there are signs of tank spilling via air box, I could only assume that something is wrong with the petcock. Check it, by removing the hose that goes from the petcock to carbs. If fuel doesn't flow, when petcock is in ON and RES, petcock functions as it should.
Otherwise, start messign with the petcock.

Check float height adjustment, as described on this site's "How To" section.

Jenya

[bryanwescoe]

Thanks, I'll try these out.  Any other suggestions?  Sitting over night there is no leak and upon further inspection it does appear that fuel could have been leaking out of the air filter (I have a K&N).

[scratch]

Also, open the oil dipstick and sniff the oil for gas.  If it smells like gas, it may have drained into you crankcase, look into the crankcase to see if you can see the gas/oil level higher than the last picture that Kerry posted here regarding viewing the oil level through the dipstick hole.

You'll have to drain the oil and gas out.

[Kerry]

the [...] picture that Kerry posted here regarding viewing the oil level through the dipstick hole.

Here's the link.  Hope it helps!