So after all of the upgrades I did to my '81 Express (carb, intake, reeds, exhaust), I couldn't get it to start moving for the life of me. I searched and searched, but couldn't find much helpful information on changing out the clutch springs on this particular engine.
I got some springs from Treatland (they're a bit short, but they work. Look for longer ones, probably 35mm):
Here's everything I used:
Harmonic balance puller
Flat blade screwdriver
New 10w40 oil
First and foremost, drain the oil out of the transfer case. My oil fill bolt was behind the kickstand area, no different looking than the rest. Removing the fill bolt at the front of the transmission speeds up the process, but there's only about a quart of oil. Also, make sure you put down newspaper under the entire length of the transfer case.
The next step is to loosen and remove all of the bolts along the transfer case. Don't take the kickstart arm off, that whole assembly comes off with the side cover and you'll have a pain reinstalling it if the spring pops off.
Find a place to start working your screwdriver in between the halves of the case and gently tap it in with the rubber mallet in several locations to separate the case evenly. A fair amount of oil will drain out that couldn't reach the drain plug. Peel off all of the old gasket, it'll never seal up right again. Spray out the inside of the case with carb cleaner next, it makes everything a lot cleaner to work with and you'll need an oil-free surface for the gasket maker to adhere well. Next is gasket maker time (unless you bought a new one). Just squeeze it on to the case half you removed and cleaned. Set it aside for a few hours so it develops a skin.
After you've finished up with your gasket, pull the exhaust off and insert a screwdriver above the piston to stop the engine from turning. Use your 14mm socket to remove the clutch nut and then attach the puller using the two small, threaded holes. The only bolts I had that were small enough were the case bolts, I believe they're m6. The clutch popped off easily with the puller and the clutch shoes were right on the back, kind of like a drum brake. I used my vise grips and some braided cable to pop the springs off, same method to put the new ones back on. The new ones were so stiff they gave me trouble stretching them, enough to make me fearful they would be too strong.
I reassembled it anyways, added new oil, and gave it a kick to start it. It revs until it hits its powerband, then it starts catching nicely. I went around to some hilly areas and was able to take off up steep hills and accelerate all the way to 30, something that would have never happened before. Now I'm not going to be so afraid to take it out on busier roads with the new acceleration. Forget drilling holes in your shoes, replaces those old, worn out springs.