Well...the short answer is, you can't. What's happening is the grease that is keeping the pawls inside the freewheel body moving freely is pretty much gone, and what is left is most likely very dry and full of years of grime and grit. You can remove the freewheel, flush it out and re-lube it with some heavy lube. My favorite is Phil's Tenacious oil. The reason why it feels "dry" is that really, it is. WD-40 is NOT a lubricant...it is a water displacement and penetrating fluid. Basically, you've actually removed the lubricant with the WD-40. The other thing you can do is simply buy a new freewheel and chain and call it good. '87 is six speed, yes? You would probably have to look around a bit, but they are out there, just make sure it's a compatible "twist-tooth" freewheel. Technically, you can actually take the entire freewheel apart and lubricate it "properly", however that is a very cumbersome job. I was never a fan of it, even as a professional mechanic. Whatever you choose, good luck!