The springs get weak and the pivot in the mechanism can be damaged beyond easy operation - even frozen completely solid - by a loose cam chain. After 30 years I doubt if any 400F hassprings strong enough that the adjuster works as described in the manual, I haven't found one.
Remove the bolt above the cam adjuster lock screw. It just plugs the hole made for the adjuster, it doesn't hold anything in. Push a small screwdriver or nail in the hole so it hits the top of the adjuster actuating rod. Loosen the lock bolt and turn the engine BACKWARDS. The rod should move upwards a bit if it's free, if not the mechanism is stiff or jammed. If it moves, set the crank to TDC 1-3. Advance the engine (forwards) about 15 degrees (the spring plate on the advancer should be just past the timing pointer) and the cam should be set in a place where it isn't pulling the chain backwards, and slack should be at the back of the engine. Now push down on the rod with your screwdriver or nail to help the tired old spring a bit, and tighten the lock bolt and its locknut. Be gentle, stripping the threads is a bad idea. Now you can try the engine and see if it's quiet, and use a bit more force if it still rattles. Replace the plug bolt when you're happy. Brute force may really quiet down the chain but will quickly wear the sliders and stretch the chain, so don't overdo it.
The original chain is prone to some stretching and should be replaced with a high strength type, either riveted (easyish job with engine in frame) or endless (complete engine dismantling required) if you want the best. A stretched chain isn't fatal but will affect cam timing. The cam chain rarely breaks... but it does happen and that destroys a LOT of expensive parts.
The tensioner sliders are still available, but may be unobtanium soon.
