Mine does that too, but it seems to work better after it's warmed up for a while.
Which makes sense... If you supply too much gas to the carb at once, it sputters (and if you're really unlucky, stalls). But after things have warmed up a bit, the carb is hot, which assists in the vaporizing part of the process, which will lead to less sputtering.
Or, I could be full of crap.
Someone will be along shortly to straighten me out if my theory is wrong.
