sounds like you have a sticky slide.

add a couple ounces of seafoam to your gas tank.

or remove and clean.

I'd like to toss in a non-expert learned-about-the-quirks-in-this-bike the hard way suggestion. How many miles do you have on the 2013? Have you done an oil change yet? The right oil makes a difference. Are you still running the stock petcock? Have you done the air screw adjustment and the white-spacer mod yet? My 2012 acted funny like that too, until I did some easy mods and got about 1,000 miles on it. Now it runs pretty good. The veterans on this site can guide you thru the -necessary- mods. Many new owners become quickly disillusioned with the newer S40's, that's why many can be found for sale quite reasonably. I know mine almost was. Now I truly love the little bugger!

WOW! 6,500 miles already? You must live on that sled! Disregard everything I said. Here in western Washington, with our greatly reduced riding season (aka crappy weather) it takes 2 or 3 years to get that kind of miles. The Vets are probably on track here. Good Luck! But on a final note myself and others have noticed an improvement in overall performance once changing to the Yamaha Raptor manual petcock, especially with fuel delivery at higher rev rates. Mine had a noticeable "flat spot" until the petcock quit altogether just over 1,000 miles. If you haven't done so already, try running on "PRI" to see if that helps. If so, then you know the culprit.