I tried flipping the spring over and just didn't care for the feel. I couldn't make it as tight as I wanted, and the throttle tension wasn't consistent (it still "clicked" near the throttle end stops as well).
The sping on mine is not symmectrical and obviously wasn't designed to be mounted "flipped over". Perhaps there are different variations of the Interlink controller.
I'm pretty sure they're all the same but then I've only seen the inside of mine
No the spring is not symmetrical, in the "proper" orientation it has a tab that slips into a slot in the case to keep it from shifting side-to-side. Flipped over that tab points up and doesn't engage the slot, so you can move it left or right off the throttle wheel. But I've found it works just fine flipped over, hasn't moved a bit. That shouldn't be a worry!
If it's not tight enough (mine was, I had to loosen it back up a tiny bit) there are a few options:
1) Like Inky says, try bending it down a bit. That would preclude putting it back the original way though if you changed your mind, unless you wanted to bend it back the other way which might
risk breaking it. (not likely to happen though...)
2) Put it back like it was and use the fuel tube option. The tube slipped over the end will get rid of the "ratchets" and you'll be able to get it plenty tight. But it will probably be "sticky". Adding some more grease might help that.
3) More drastic measure but sure to work. Leave the tab flipped upside down, and use a good sharp chisel to carefully shave off a small
amount of the post that the tab screws into. This will lower the tab relative to the throttle wheel and allow more tension. You can easily put it back the way it was later if you change your mind, by placing a washer between the post and the tab to make up for the material you removed. If you want to do that, the secret is to remove a SMALL thickness, put it together and try it out, and only remove more if it's still too loose. And by "small" I mean paper-thin
Good luck, and HTH! I love this mod, it makes a world of difference flying heli's
Hope you can get it working to your liking!