The Frame mounted vacuum operated petcock allows fuel to flow down through the carb and into the airbox and drains out the airbox drain line.  I am not leaving the petcock in the prime position when this happens.  I first noticed this on the the first few cold nights in Florida after buying this bike used, and it has done this to me intermittently ever since.  I have replaced the petcock with a new OEM petcock, same result.  I have opened up this new petcock and verified the diaphragm is good and there is no debris, dirt or build up anywhere inside.  I am currently rebuilding the carbs to correct the fact the fuel continues to flow even after the bowls are full, but the with the petcock in the ON or Res positions, this should not have been a problem.  My question is, Why does this petcock intermittently allow fuel to flow when it shouldn't, and when there are no visible signs of a problem with a bran new OEM petcock.  It is almost as if a vacuum is getting applied intermittently while the bike is off, and it seems like it might be somewhat influenced by colder weather.  Any help out there will be appreciated

Quote from: MorganScott on February 25, 2017, 01:18:08 PM
*snip*

okay well, I also live in Florida, and my OEM petcock also leaks from the petcock, when its colder outside, and the leak slows/stops when its warm.. I think its related to the gasket under the switch itself, and not the diaphragm.. but good luck finding a replacement to that stupid thing.

Thank you for the response, mine has never leaked from the petcock itself, but through the petcock allowing fuel to flow down to the carbs while the bike sits overnight.  I guess it's possible the seal inside the petcock isn't tight enough to allow fuel to flow from one chamber to the next without the plunger being open, but I don't think that would explain the volume I am seeing.  I almost suspect that the vacuum isn't getting released properly when the bike shuts of, or that the warm air in a closed system contracts causing a vacuum.  For either of these to be true, something has to be blocking the flow of air that would release the vacuum (i think) but I don't know where to look to see if this is what's happening