I had a similar problem, but only with one carb. Removed the bowl, and then the whole carburetor.
Dumped it (fuel) all through a coffee filter and found just the smallest piece of dirt in the bottom. Cleaned all the passages and put everything back together and the problem was solved.
Was anticipating a big problem (floats/carb setup/sync) but ended up to be minor.
Sometimes installation of a new fuel line will introduce debris if not careful.
Luckily we have folks like Roger Lee and Rob Seaton on this site!!!
Hopefully your problem will be as simple!
Ron
