250 vacum source

[NicoSlam]

So I finally replaced the dampner on my 250 over the weekend so I attempted to timing it using the light. I disconnected the vacum line from the distributor and plugged it. I set the timing accordingly (0TDC with standard). When I reconnected the vacum line I noticed there was no change in timing at idle. I disconnected the line again and tried to feel for vacum (using tongue) from the carb but I couldn't. The carb is an original monjet. Is the vacum that suttle? what should be the vacuum at idle (950rpm)? Honestly, I was expecting a hissing sound and a very obvious shift in timing with and without the line connected to the distributor.

Thanks for your help.