I got a set of stiff springs for Tomos and having never changed the springs before found it to be quite a challenge with heavier springs. I found a method that seems to work pretty easily, so here it is. The first thing the performance springs needed was to bend the ends to match the black stock springs.
I put them barely in the vice and used my hands to bend the spring carefully by the base until the ends were standing up like a hook. Once I hooked the ends together I squeezed them a little tighter so they wouldn't easily come apart.
I clamped the second speed clutch by the attached gear, and used a bolt to hold the first speed down.
Then press the spring into the first keeper and install a locking pliers. It doesn't have to be that tight. Push the spring into the second keeper and install your second locking pliers. I installed the hooked section of the spring in the middle of the first and second keepers. Take two long flat screw drivers, round shaft work best, and set them against the clutch arm right on top of the third keeper. Pull the screw drivers back gently and the spring slides down to the top of the keeper.
It's all in the placement and rotation of the screw drivers. If you set them wider apart you can't get the spring to fall into the slot because there isn't room for the screw drivers to be out of the way. By placing the screw drivers against the shoe, it is solid and won't budge against them, but if you try to pry against the keeper you are going to bend it and have a bad time. The little twist pushed the spring out to clear the keeper without having to pull on it any more. Easy as pie.