Originally Posted by
cdmurphy
Your freewheel probably just needs lubing. I haven't seen a NOS Suntour, but they probably just used a light oil. (Which has evaporated). You don't want grease in there, unless you're careful to keep it out of the pawls. (if the grease gets in the pawls, it can slow their engagement, potentially leading to skipping and poor engagement.) Usually, I dribble heavy gear oil into my freewheels. It gets were it needs to go, and sticks around a bit better than lighter oils.
It's also possible the bearing adjustment is simply too loose, but suspect it's just dry.
+1
DON'T GREASE IT!
Light machine oil, as noted, is the best lube for freewheels of all kinds, Suntour freewheels especially. Unlike every other bicycle bearing, freewheels only spin when they are under no load. So the bearings don't need the heavy lube that grease provides. The bearings in freewheels function mostly as spacers to keep the pawls engaged in the ratchets when loaded. But they are static when that happens. The freewheel is moving with the hub, and is essentially part of the hub.
If grease is used the pawls can get stuck in "open" mode and can turn into free-as-a-bird-now-both-ways-wheels. Suntour freewheels in particular were susceptible to this. You can pretty much run a freewheel with no lube and it will function better than with grease in it. It won't last super long, but it won't spin both ways.
It is possible that the adjustment is a little bit loose. Since you have an Ultra spaced Suntour FW, it's likely to be some sort of Winner. If you have New Winner model, you can adjust the bearings if you have the right tool. It adjusts kind of like a hub cone. If you have a Winner or Winner Pro, the adjustment is with shims. If you don't have the tool or shims, best to lube it and ride it. It should be just fine.