Usually my '85 2.8 starts right up with just a tap of the key. Other times it takes several seconds to start and it slowly winds up before it fires. And still other times it stumbles while cranking as if the timing were off. But once it starts it runs fine. Ideas?

I'd start by checking out the fuel pump relay. A common troubleshooting technique is to swap the electrical plugs on the fuel pump and A/C relays. They're next to each other on the firewall. See if that changes anything.