Yes the poppet is open slightly when the throttle is set to off, it is supposed to be this way, you are cutting the engine off, not starving it. Why would you even been trying to make it run in the off position?
The critical point about the 'stop position' of the LM carby cam, is that the poppet valve is
not the only component controlling the air flow at this throttle position. The 'cam arms' close off the peripheral slots in the 'air chamber' under the cam.
This is an issue that can't be explained properly without diagrams; it really needs a hard copy of one of the workshop manuals in front of you. The online downloads just don't have sufficient image resolution to make out what's going on!
