Engine Sputter on 03 YZ450F

BTW, this is a street legal supermoto bike.

I am hoping someone can shed some light on my sputter problem. The engine always starts right up. It always runs great when you're applying throttle. Problem: when at a cruising speed and approx 3/8 throttle or less, the engine sputters every second or two. As soon as the throttle is applied, it runs strong with no sputters.

I just bought the bike today so I don't know any of it's history. It has a full exhaust and was told the carb has factory jets...I can't verify that. This bike came from Arkansas so I'd imagine it needs some jetting changes for the different altitude. What do you think?

does it do this in a certain gear by any chance?

you could just clean the carb really good and try it again. if it only does it in a certain gear(or two maybe) you might have tranny trouble.

I think it does it in all gears. I'm pretty sure it's an engine miss.

At that low of a throttle opening, the pilot still has a significant influence. You might try fudging the fuel screw out (or in) a half turn to see what happens. Could be slightly lean at that point. A lean misfire should be kind of irregular. Rich is usually a more regular sounding stutter.

I'm not too knowledgable about carbs but the previous owner said he messed with the fuel screw (on the bottom, front) with no luck. What about a jet kit? It did come from Arkansas.

I can install this jet kit and problem solved?


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