Mercury 1985 outboard 35 HP
Bought it used.. fresh gas, plugs and fuel filter. The engine starts fine
and idles fine in the driveway.

(yes gas vent was open)

We took it out this evening wheneve we tried to give it some throttle, it
would bog out and die. It would move foward but at a slow speed. When we
played with the choke (moved it halfway) we could get the boat moving well.

Any clues as to what to look for?