well i've had a play and all is not well
after following the haynes manual i removed the carbs the long and difficult way. got the tensioner out and it looked like this.
its spotless, no gunk, moves freely, little to no wear. i cant push the tensioner back out by hand without releasing the ratchet. i counted 8 notches.
when pushed all the way out it looked like this
i counted about 13 or 14 notches at its maximum. so i don't think the chain is beyond its wear limit.
on the advice of a bike mechanic friend i added an extra bearing to increase the spring strength. i didnt have a bearing but used an m3 nut instead in this order.
i then put all the relevant bits back on etc etc and rode the bike home. as usual within ten mins of riding the rattle was back
balls!
so earlier today i decided i would manually advance the tensioner by one click. got the carbs off again, this time without undoing everything as haynes suggests and just lifting them up out the way. as i put the tensioner back in (now adjusted by one click) it seemed tight before it reached the engine block, the bolts pulled it in the last 3mm or so.
everything back on, cracked her up and within ten mins engine is rattling away again, no change
balls again!
now i have to repeat the whole process again to return the tensioner back it its correct auto adjusted position.
so i think i can safely rule out the cam chain tension as the problem?
so if its not cam chain rattle, what else could it be? valve clearances?
by the way if not already mentioned bike is just under the 20000 mark. sorry for the huge pics!