The vacuum is ported, so it is shut off at idle. That can be verifed with a vacuum gauge T'ed into line. Adjusting timing to 34 to 36 with line on, may result in retarted timing for cruise. This may will result in overheating, poor mpg, poor throttle reponse. If you are going to set at 34, do that with line off.
I also belive performance timing is not a adjustment at a single point. It is a 3D table for the full range of RPM and vacuum. That takes a programable ECU.
