Pre-diagnostic-era M103 duty cycle

[ps2cho]

I found a lone vacuum hose unhooked below the fuel distributor and ever since I plugged it back in, the car is taking an extra 1-3 seconds to start up cold and I also think my mpg has dropped based on the fact I am at "empty" and only at 265mi when I usually get about 280-290mi before it hits empty. When I fill up tomorrow afternoon I will get an accurate reading, but nonetheless its still starting slower.

So maybe the fuel mixture/duty cycle needs a tweak towards leaner?

What is the CORRECT procedure to check the duty cycle on a car WITHOUT the diagnostic port near the battery? Do I simply probe the X11 when the car is warm or are there any preliminary steps to take? On my 88 california 300TE it requires preliminary steps, but she has the diagnostic port so I have always followed the

The readings before were a little finicky that is why I am asking the question to check I am not missing any steps at all.

Thanks,
Robert