Topic: Help!!! Engine under vacume?

[seanplarkin]

So my bike runs and is functioning, but when i turn the switch off and the engine is off, when i open the oil tank cover i hear a sucking sound is this normal? 

[mystic_1]

Generally no.

What bike are we talking about?

mystic_1

[seanplarkin]

1974 cb750 k4, no oil cooling unit...

[Markcb750]

Sounds like the crankcase vent is plugged and as the air in the tank cools a slight negative pressure is developed.  check the line off the center of the valve cover.

[seanplarkin]

That's what i was thinking. would this also effect the engine idle speed and low idle?

[WFO]

The sucking sound is money being extracted from your wallet 

[seanplarkin]

Now it is actually building pressure, is that normal?  I turn the engine off an i can hear a hissing noise of air escaping, i have a pressure gauge on the bike and it is operating around 60 psi, is this normal?

[mystic_1]

Now it is actually building pressure, is that normal?  I turn the engine off an i can hear a hissing noise of air escaping, i have a pressure gauge on the bike and it is operating around 60 psi, is this normal?

Your oil pressure gauge is measuring pressure downstream of the oil pump, between the pump and the sump.  The oil tank is not part of this system.  The tank is supposed to be vented and should not have any pressure inside.

60psi is reasonable for a 750 at startup, but actual pressure will depend on the operating temp, oil viscosity, etc.

mystic_1