Can anyone tell me how much preload I should put on my 240 kickstart return spring when installing it? Thanks.

There are 2 springs which control the return.

The one i think you are talking about is inside the main gearbox (the other is under and behind the clutch)and as you look at it is hidden behind gear cogs.

As i recall the spring should be revolved once and them slotted into place and no more. Terrific tension is not needed , just enough to lift the kick start back . If you try twisting it any more its difficult to slot into place.

Its a difficult one to describe , but i hope this helps.