When I shut my bike off when its hot, it makes a percolating sound for 20 minutes or so. It sounds like something is gently boiling within the engine.
At first I thought it was the cooling system, but came to realize its actually the fuel system making the noise. If I remove my gas cap the noise goes away entirely. Furthermore, if my tank is half full and I look into the tank, I can see bubbles coming up from the bottom of the tank.
This can go on for quite a while. On one ride the fuel was still making this noise after I had undressed, packed up and we had loaded 2 bikes onto my truck. At least 15 minutes.
At first I thought (and was told) that this is fuel leaking back from the high pressure side of the injection system (ie between the pump and the fuel injector) into the tank. But the more I think of it, the volume of fuel to release that pressure should be pretty small and it shouldn't take anywhere near 10 minutes to do so.
I'm wondering if others are seeing and hearing the same thing or if its just my bike.
I'm wondering if the fuel percolation is caused by boiling fuel in the fuel line between the fuel pump and the injector.
This season my bike stopped starting on the first kick. I also installed a higher pressure rad cap (2.1 bar, 30 PSI) at the start of the season. I'm wondering if the two are related.
An interesting tidbit of information possibly related to this issue is that factory KTM race bikes have their fuel injection line insulated and wrapped with a metal foil to keep the heat out.
Observations, comments and advice ?