I have a Fox 35 I bought new, mid eighties model. It was very, very tight. It wouldn't spin freely with the glow plug removed and the backplate loose. It would run for a second or two and then stop. In the end I had to hand lap the piston and cylinder to get it running.
I am not suggesting you do this, not at all, but you might have a tight Fox. If so then keep plugging away, it will start. Keep it rich too.

Edit: Hossfly's advice is very good, worth following.