I bought a 95 Yamaha Wave Venture 700 about a month ago. Ran great! Ridden several times with no issues. Then all of a sudden my son had trouble starting it. So I went out and played with the throttle and choke and finally got it to start. But it ran like crap. We changed the spark plugs and fuel filter and now it starts right up, runs decent all the way to about 3/4 throttle..Then it starts to stutter and run crappy. What do I do next? Carb clean? Carb rebuild? I'm at a loss of why it would do that all of a sudden.