Originally Posted by seagull
The burp when cold is for Rotax engines mounted in other planes, such as taildraggers with Bush tires on them. Sometimes, this configuration causes problems with the fuel floats in the carbs, also, since the engine is not close to being level.
In some situations, such as on some Kitfox builds, the sump tank is mounted so low on the firewall, such that the oil can syphon back into the engine or back cylinder heads and cause hydraulic lock.
So turning the prop after sitting or in your hanger, ensures that there's no hydraulic lock that could bend connecting rods or do other damage to your engine, before you use the electric starter.
I do get two different readings, if I only burp when cold, it's shows up lower on the dip stick, sometimes as much as 3/16 to 1/4 " difference.