I have a 1984 Big Red and it runs fairly ok for the most part, always seems to run rich no matter what I do to the carb screws, smokes a tiny bit when idling (smells horrible, hurts my nose), and occasionally moves without touching the throttle. Now that all that is out of the way here's the "occurrence" that is kinda annoying, my driveway is pretty long and downhill and I down it often, and when I go down hill I am coasting in neutral, but when I reach the bottom of the hill, my Big Red starts revving harder and harder until it sounds like it's pinned and then I have to turn it off because if I put it in gear I will fly onto the road which is very busy, and after waiting a minute or so and I start my threewheeler up again and it runs fine with no revving. This isn't a huge problem but it is very annoying and I have no idea what would cause this. Any ideas?