Complaint: "Only runs on one speed - HIGH and it sounds like its going to explode. all else is fine"
First thing I noticed was an added lightweight spring to return the choke to open position. OK, seems like choke return spring may be broken.. so we pull the top off the engine for a better look.

Well obviously someone's tried to fix it.. do you see the problem?
here's a better shot:





Originals are here if you want bigger photo to look at:
http://i465.photobucket.com/albums/rr13 ... /003-3.jpg
http://i465.photobucket.com/albums/rr13 ... /004-2.jpg