Standby Vacuum performance w/ PC system

[danb35]

Yesterday my mechanic and I took a flight to check out the Precise Flight standby vacuum system in '48Q, and weren't too happy with the results.  At 2000' MSL, the throttle needed to be retarded to about 15" to produce adequate vacuum (according to my vacuum gauge).

Before engaging in extensive troubleshooting, I'm wondering if the plane's equipment could be causing the poor performance.  According to the documentation, the system is only intended to operate two instruments.  Well, '48Q has three vac instruments (a backup AI on the right side panel, in addition to the primary AI and DG), and it also has the Brittain B-11, B-12, and PC autopilots installed.  The B-11 and B-12 can be switched off, but the PC is full-time.

Is my problem simply that I'm trying to drive too much stuff with the standby vacuum system, or should I try to find another problem?

[The-sky-captain]

I'm kind of going through the same issue. I've got the Precise Flight system on my plane but have no placards with what engine settings to use at certain altitudes. Do I need to disable the regular system and go fly the plane using the standby system to do this?

[danb35]

To determine this, you'd disconnect the vacuum hose from the vac pump and attach a filter (to keep contaminants from getting into the pump), and then go fly.  If you don't have placards, I don't believe your installation is technically airworthy.