Originally Posted by grizz1

Yep - your onto it

The pinch test actually has two purposes.
How much the motor revs up when you pinch off the fuel line - tells you if your idle gap is too big or not.

How long the motor runs for after you pinch the line off - tells you if your LSN is too rich or too lean.
If the motor stops in a couple seconds, you are too lean.
If it stops between 5 and 7 seconds you are pretty close to correct.
If it runs on for longer then 7 seconds you are too rich.

Once again this needs to be done when the motor is not too hot.
Once the motor is up to normal running temps, a 5 - 7 sec pinch time will drop to a 2 - 3 sec pinch time, plus the revs will come up higher as well, due to the crankcase being hot and evapourating / atomising the fuel more effeciently. Which is why you should only fully tune a motor for performance when it is hot, as these are the conditions it will be running under on the track.