Im having an issue with my port engine..I have twin 420 HP 454 Mercruisers in my 87 Formula..this boatnis new to me this year and the port is my problem child as it would stall when trying to put into gear and i couldnt get her over 3200 RPM at WOT..noticed that the mechanical fuel pump was pumping fuel up through the tell tale tube so I changed out pumps..still had the same problem and it was backfiring and starting hard so I timed it and did some carb adjustments..still hard starting and backfires but when is running runs strong (as it has through idle to 3200 RPM) and now doesn't stall going into gear..checked fuel filters in Holeys and were clean..new separator filter before all this..when actuating the throttle by hand and looking in carb the secondaries open fine and pumps plenty of fuel into carb at WOT (not running obviously I still have eyebrows) my next step is to change out the cap rotor and timing advance sensor and hope that helps but I am at a loss short of rebuilding the carb..anyone have any suggestions? Any and all help will be much appreciated!

One more thing..Stbd runs like a gem..no issues whatsoever with her so not thinking its fuel related

I would pull the spark plugs an ck compression. If the compressions good replace plugs an go from there. You will know more about what Your working with after You do this. The extra fuel may have fouled some plugs.

Forgot to add that..I have replaced plugs as well..but havent done compression check..YET

Do the compression check you may have a valve issue.

make sure your not still dumping fuel into the engine,,stuck float..also change your oil,,,or al leaste check it for being over full from the gas dumping in the carb....that will slow down a crank from spinning..