I am a new owner of a 1977 Honda Express, it starts/runs pretty well give or take some adjustments with the idle and maybe some cleaning. The real confusing thing is this: it gets up to 27mph pretty easy and stays right around there. When I go down a huge hill it will get upwards of 30-35 mph but often times after going at such a high speed it will lose power right after and inevitably stall. Usually if I turn it off and let it cool down, walk it a block it runs again. If I try to start it right after it will start but won't rev well, loses power and inevitably stalls again. Any ideas dr.s?