pro 50 not pulling fuel

Hi all, Im having a problem with a 1991 pro 50 outboard. When I go to accelerate there is no response. I went in and rebuilt the carbs and did a lync and sync, and set timing. I still have the same problem.( no accerlation and back firing through exhaust) I have checked fuel pressure, installed clear line to look for air, checked reeds. Long story short, carbs gone through several times (no problem found) rechecked timing, 125 lbs compression on all cylinders. I had this simular problem with an inline mercury where i had to replace the sealing rings on the crank. Before I start tearing this engine down is there something I might be overlooking? TJ

[boats.net]

Could be misfiring on 1 cylinder or a bad reed.

Thanks for replying, I have ran several spark test to make sure spark was consistant. I guess the only thing left to do is tear in to this machine and see whats shes made of. Thanks again TJ