I had a problem similar to yours with my 83 a few months ago. Turned out to be a bad solder connection on what I have heard called the tip over switch. You can get to it through the headlight. With the bike idling I was moving the wires behind the headlight and I moved the right one and it speeded up and idled smooth. There is two for sale on ebay now if you want to see what it looks like. Hope this helps as mine was a easy and no cost fix.