1981 gs1100 fuel question

[alhntr]

Hi guys, Just recently purchased 1981 GS1100. This may sound like dumb question for you all. The fuel petcock has three positions, fuel,reserve and pri for prime. What is the purpose of prime? Which position do you leave it in when not in use. I'm used to dirt bike that has a off position. The point on handle points toward botom of tail of lever, or does the other end point to desired postion. Also my air box cover lid is missing....is this anything to concerned about? Anyone use the MotionPro or EMGO carb sync tools ? Will be rebuilding my carbs when orings and bowl gaskets arrive. Thanks

 

[Wallowgreen]

There's a diaphragm inside the petcock that acts as a small pump, it's driven by the vacuum from one of the carburetors. When in good working order, the petcock will only pass fuel in fuel and reserve positions when the engine is running. The prime position is like a bypass so will allow fuel to flow when the engine is not running. I leave my petcock in fuel or reserve, fuel should not flow in those positions. However, there are many threads that talk about fuel flooding the carbs and getting into the engine oil. This is often due to the petcock being in poor condition allowing fuel to flow in fuel or reserve positions when the engine is off. There has to be some compounding issue inside the carbs with floats or needle valve as well for it to flood and contaminate the engine oil.

Not used the sync tools you mention so can't comment on those, I use the Carbtune version.