rfw2003 wrote on 07/09/12 at 16:35:57:Correct me if I'm wrong here, but even if it was leaking by the float needle or seat, this would only really happen with the petcock open, because the pressure of the fuel from the tank would make it leak. With the petcock off there would be no way for it to leak past since the fuel level in the bowl is lower then the float needle/seat there by leaving fuel in the bowl unless the bike was laying down or upside down.
You are correct. With the Raptor petcock in "OFF" position or OEM petcock de-energized (engine off - no vacuum), the float bowl would normally not drain.
With high temperatures, fuel could evaporate quicker. (California model has a charcoal canister, don't know if this would help reduce evaporation.)
Where the concern comes in, is when the engine is not running, with a manual petcock in the open position or failed OEM petcock, fuel flow from the tank is by gravity. If the flow bowl needle valve is leaking or float is set too high, unable to shut the flow completely, will cause the bowl to overfill, flow past carburetor throat to the combustion chamber.
In an automobile with carburetor, fuel is supplied by a low pressure fuel pump (mechanical or electric, less than 15 psig, usually around 7.5 psig). Due to the fuel tank being lower than the carburetor, there is no flow when the engine is off. Needle valve leakage is less evident and less likely to harm the engine.
Using the OFF position on a manual petcock is therefore a necessity to prevent potential disasters.
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