2006 Suzuki GZ250

[Project400]

I just bought my bike from a dealer a few weeks ago. It's a 2006 and it had 17,000 miles on it. I had it out today for a cold ride – maybe a half hour or so – I stopped at a beach for a minute or two to warm my hands and on the way back, the bike wouldn't go over 20 mph. It felt as though first gear wasn't very powerful and needless to say, the other gears weren't an option. Might this be a gummed up carburetor? Something to do with a cold weather? I know the fuel was treated when the dealer delivered the bike. Could this be a clutch issue? If anyone has any information it would be most appreciated! Thanks.