81 xs400

Hey guys, Just picked up a cool xs400h. Bought it not running but got it to run this weekend. Ive got a few issues with it. At first it would not idle but gradually came down to a steady smooth idle at about 1200rpm. I took it for a quick ride and It has a high rpm studder that seem like a revlimiter at about 6200rpm. Timing? carbs? few things to note here...the timing was really screwed up and I had to turn the tci pickup untill I got the bike to fire. The bike has been all apart so im guessing the guy that put it back together didnt know what he was doing. That being said how do I check the timing? or more specificly where do I shine my timing light when I hook it up to the left side cylinder? (cant find a clear answer in the manual) Next up...the inside of the tank is quite rusty. I have a clear fuel line and a small inline filter on it now and I can see im getting some serious rust out of the tank. Its not scaling rust or anywhere neer rotting through but patchy light rust on a an otherwise bare metal surface. I hear many tricks can be used to clear the rust out of the tank...are there any that work best? I hear yamaha sells a chemical kit that nutralizes it? Lastly, the bike has 2 to 1 ehaust with a small muffler and UNI pod filters, can any one advise me on what I should do to re-jet the carbs...or should I wait and see what the spark plugs tell me? I have not ridden the bike much but if I need to clean the carbs to get rust out I'd like to rejet while im in there. this bike will be a dailiy driver/commuter this summer and im hoping it will treat me well thanks in advance for any advice! (ill post some pics as soon as I take some)