the qj carb has mechanical secondary linkage with a secondary air valve.

Also tuning the carb the boat needs to be in the water and in base timing mood if in fact you T bolt V ignition set up. Mercruiser has a lot info of tuning these carbs even in a video and a mini manual all about the Q jet only.

If its a 350 Mag with a G-Jet , Its a mid 80's Right ? Pop through Carb is Lean Pop , Low Timing , Incorrect Accel Pump Adjustment , Low Voltage to Ignition , Could be A Low Float Level . Those old Q-Jets are not a DIY friendly rebuild , Just sayin . Secondary Air Door needs to be correctly tensioned .
Especially on a Boat.