Mercury 7.5 1973 Blowback, ok reeds

[Bosunsmate]

Hi, Im trying to repair a Merc 7.5 hp serial 8004212. It had weak spark so i replaced the insulators and wires and spark came good. It still wouldnt start so i put fuel in the spark holes and it went great for a second or so. i noticed that it had some blow back into the carbs. I was not expecting to have to take the engine apart to get to the reeds. I also had big trouble with the use of philip screws to hold the crankcase together. But be that as it may, i got it apart and the reed valves look great! From what i have found out from reading other posts the reed valve unit fills with oil which seals the crankshaft between the different cylinders so there is nothing to replace in there, but i do have a bottom cylinder that looks as though its running dry. It has rust on the piston,the bottom bearing was dry, the top bearing wasnt. Also the bottom engine seal looks slightly worn but i dont know how that can cause blow back into the carb.
I checked the reed valves and they are closing properly.
Any suggestions?
thanks