Ok well I had a look at mine, and as it is the early model it has the shorter B56, after looking through the IPL's yours should have a b59. Is it only falling off when disengaged? I did also notice an adjustment on the disengage arm on that model, check if it has been played with. Apart from that if everything else is right and you're spring is good, I don't really know what to suggest. All of the IPL's definitely show the engine pulley having a very large bottom sheave, there was only ever a retainer on the deck pulley, I think I noticed you're pulley had some damage in you're other post, could that be something to do with it?
