I have a 94 (off/on/res no prime) petcock. The bike recently started running poorly and then wouldn't start. I disconnected the fuel line from the petcock valve to the carb and cycled the valve between positions. I got no fuel and the line seemed dry inside. However, I'm not sure how the vac valve works (where it's vac source is,how it works) so I'm not sure if that's normal and I just need to apply suction to the valve somewhere.
Also, I thought the other 2 lines were feed lines but it appears the valve is actually partially in the tank so I'm not sure what the other 2 lines are.
No vacuum specs that I can find, or have heard of.
No fuel pump or fuel pressure spes either, just gravity feed once vacuum is applied to middle nipple on petcock..
Petcock has 2 fuel nipples, one on each end.
To check for a dirty screen or plugged pickup tubes on petcock, pull the fuel lines off the carbs and stick ends in a clear jar. Check vacuum line for cracks and tight clamps, then crank engine over to get vacuum. You should get free flowing gas into the jar in a few seconds.
You can drain the carbs of old fuel through a hose into the jar too, by loosening the screws under the drain nipples. Hook the fuel lines back up to the carbs and crank the engine over again. If you get fresh fuel flowing out the drains again in a few more seconds you know the carbs are getting fuel.
If there is no fuel flow then either the vacuum source diaphram in the carb is faulty, or the petcock vacuum valve is faulty or the tubes are plugged up.
Hope this helps.