Pinskas,
The vac petcock on our bikes has very marginal operating parameters (when it is new it just barely makes it work at full speed). Our bikes do not have any excess vacuum level amounts to actuate the thing correctly once the diaphragm gets old and stiff.
People are trying to get you to go through the steps to say:
1) the problem is the vac petcock (although they already know it likely is)
2) teach you how to coddle the old dead thing along month to month to keep it going (that's your clamps on vac tubes, replacing vac tubes)
3) offer you emotional support as the many versions of petcock symptoms drive you crazy over time as the ongoing list of failures outruns your repair attempts.
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There is a growing group here on the list that thinks the very first thing you should be told to do is to tear off the trouble prone stock vac petcock and replace it with a manual Raptor petcock.
The reason we feel this way is there are many levels of different vac petcock issues that strike in series, with the final one being that the durn thing splits and leaks gasoline down your carb vac line and contaminates your lubricating oil in the sump -- sometimes doing damage to your engine in the process. This is after being a bleeding hemorrhoid to live with for years -- it finally tries to kill your engine.
This "gas in oil" thing was once said to be very rare, but since I have ticked 4 occasions inside the last 12 months I no longer consider it rare -- it is to me a potential "likelyhood" if you run your vac petcock long enough.
Even the vac petcock fans (of which 3 vocal ones still remain) admit that some of them have replaced their diaphragm and are still having to replace their vac line on a yearly basis.
The 30+ folks who have gone over to the Raptor report NO PERFORMANCE ISSUES AT ALL so far and NO ISSUES WITH GAS IN THE OIL. We find this very interesting and are waiting for the first "oil-in-gas" to find out how it actually occurs.