A few years ago I bought a 1978 Solo Odyssey 2 speed. It runs great for short distances but after a minute or so it accelerates on its own, then slows down, then accelerates again, etc- all this is happening but I'm not doing anything with the throttle. When I ride on hilly roads i noticed that it wants to go wide-open on downhills and kind of dies off on the uphills, sometimes completely just shuts off on larger hill climbs. I guess the best way to describe it would be like if it had cruise-control but its doing the opposite of what it should be doing to maintain a constant speed on hills. It wants to keep going when I try to stop. Its not the throttle cables, I had new put on recently hoping to fix this problem but its something else. Anything anyone can tell me would be greatly appreciated.