I am having a couple different issues with my engine. The first being that it will typically start, but will not keep running. It will idle, but as soon as it goes in gear it will die. It doesn't really matter if it's cold or has warmed up. Eventually it will keep running, but it make take 4 or 5 times of restarting. The second issue is that the engine doesn't seem to be running well at all. At full throttle it only tops out at around 5 mph, where as a couple of months ago I was hitting 50 at W.O.T. Any idea what could be causing these issues? I've thought about replacing all the spark plugs, but didn't have any other ideas as to what could solve these problems.