There should be no access point for you to put a gauge in-line with this system. As with all engines, eliminate the easy things before moving into the carb. Timing & spark, plugs, dizz advance operation, rocker clearance, compression and leak-down. Concentrating on secondary action at this point is getting way ahead of things. Do you know for certain that it is not running as well as the day it was new? Small engine + auto trans = get comfy cuz this trip up the on-ramp will take some time.