Using an old Sunpak slave flash.

[mongoose]

I got an old Sunpak 144PC flash from my father that I'm trying to figure out how to use with my Nikon D80. The flash has a PC cord with a "Sunpak Slave Unit" device plugged into the end of it. The flash head can be turned 90 degrees from straight ahead to straight up.

Now, maybe I'm imaging this, but does the flash operate different when turned upwards? When I keep the head angled straight ahead, it works fine for me. When I point it at an angle though, I can see it flashing but sometimes it doesn't show up in the photo. I figure it's either not putting out enough power to show up in the photo, or it's going off out of sync? It doesn't consistently do this though, sometimes it works fine, sometimes it flashes and doesn't show up.

Edit: More Info
I found out something else. When the flash head it turned straight forward, the flash always goes off as a slave flash. If it's turned up 45 or 90 degrees, it always goes off but only if I wait 30 seconds after the ready light turns on. My guess is it's not charged up fully enough for the slave sensor to react quickly enough? But then why would it always work fine when it's pointed straight forward? I need money to buy a real flash...