That is a great question, I suppose I can open up the manual, and double check, I was only studying 2 college classes, and I am always looking at procrastinating for those classes. I am going to click on the Tech tab, at the top of the screen, and see if we have that info already there. My memory is so fuzzy about the details, I can tell you if I had in my hands, but with soo much going on since I just put it together 2 months ago, I have forgotten. I sit there and figure it out, in my hands. There is a picture of someone who put in on 180 degrees from right. (backwards) couldn't figure out why it didn't work right, then when we seen the pic, The first response that it was obvious, but If you don't know, then neither did he. I think. It was a funny story, because I wasn't the center of the story. Wow that didn't take too long, it was the 9th one on the list. I think this thread will help you, now to nominate a thread to put this on to the "Tech Page" The other option is the 2nd sticky down on the garage forum, has something marked "Yamaha XS400 manuals" There are 2 basic manuals, pre 1982, and post 1982. Everything built pre 1982 was considered SOHC, and the post, is DOHC. (their may one or two exceptions) So the one marked 360-400 is for the SOHC. Page 16 has the short instructions for doing. with one pic, pretty useless, It just says pull it out, and then put it in, pull spring clockwise. and put it on the projected piece of metal, come to think of it, I replaced my sping last year. I suspect since I am 600 miles from my home, and can not see it, I suspect that the lever needs to go counter clockwise, so the lug will need to be up against the block that is clockwise from its current ready to kick position. Does that make sense? You know ever since the invent of digital watches, no one knows which way clockwise is.
I suppose I was hard on you, sorry, we literally have 4 years of tech knowledge on this website, I know the info is here, once you open it up, it will make sense to you. Before you go that far, YouTube the kick start installation old Yamaha, I couldn't find anything specific for our bikes, but don't let me stop you from looking.
http://www.xs400.com/forum/showthread.php?t=10050&page=2