no suction at bottom carb

[felderlostnspace]

i have a 1978 mercury 80 hp,model 8oo outboard.i can get it started after a while and sometimes putting gas/oil mixture into the carbs.after it is running i have no suction at the bottom carb.i have good suction at the top carb and can see gas going down the throat of the carb.i have checked the compression and it is right at 115 on all 4 cylinders.any help would be great.thanks in advance,Bill