vacuum readings question
I am fine tuning the holley 390[there when I bought the jeep] and the DUI [just purchased] and have some weird vacuum action. Was wondering if anyone had any thoughts or possibilities to share. My initial timing is @ 8* and with the carb tuned off manifold I had it all setup with a very nice 19.5-20 " when warm then I noticed the gauge fell to around 15" and stayed there. Thought this was weird and started looking for leaks with propane and things and i couldn't find a leak. I glanced up @ the gauge and it was reading normal again [19.5]. I figured that me tightening things on the manifold musta fixed the leak or something and thought i was good to go...A few days later i was drivin round takin ptc readings inside my cab to ascertain which power valve to use and when i was on my way home the vacuum dropped down again to the 15" mark and stayed there all the way till i parked in me garage. Now im confused by this reading as it appears to be intermittent, so the charts of vacuum readings have me going in many different directions. Anybody have any ideas here as to what might most likely be the best direction to look at? Anybody have this intermittent thing b4?