Scooterotica

Help, I'm currently baffled by my inability to select 2nd gear and a very rattly clutch. The engine is newly built, using a SIL 200 casing and low milage innocenti Li Special innards and a mint TV175 gearbox. The gearbox is shimed correctly, endplate torqued down correctly, chain tensioned to 5mm play, new clutch plates etc. The cables are also adjusted correctly. When the engines cold its very quiet, but after 10 mins it develops quite loud rattle. Ive checked the kickstart teeth and they are not engaging before they should. The gear problem is a real pig, from neutral to first fine, but up into second and I either hit a false neutral or go straight into 3rd. Up to fourth is fine and back down the gears, including 2nd is fine. I've stripped and rebuilt the box once just to make sure I didn't put 2nd the wrong way round. Any suggestions greatly appreciated!