i have a 97 sportster the engine will start but runs rough try to give it gas and it dies, the other day it ran good for about 5 minutes then it died and would not start, then the next day on the trailer it started but did not run very well, having a problem trying to figure it out, also does my boat have rave valves? it has the 720 engine in, it has good spark and fuel, any help is apperciated.