Lower vacuum at initial start up

[1arch]

Last year my vacuum was <25" (no lines connected) at initial start up but eventually increased to ~27+ for the season. Today I started the vacuum pump for a discouraging 20" for over an hour until temperature fell to below freezing. Are lower vacuum levels typical until the vanes seat themselves for the season?

[maple flats]

Not that I'm aware of. Did you change the oil in the pump? The oil in the reclaimer should be changed at least every 2-3 weeks max, and always start the season with fresh vacuum oil.
You might have a few leaks in your tubing. If the vacuum rose at freeze up, you may want to check at the taps.