I have a 79 century arabian with a 305 merc with a 898 outdrive. Well i have had a excellent tune up replaced all the fuel lines, pickup tube, check valve, both fuel filters, plugs, cap, rotor, dwel land points set correctly, carberator rebuilt professinaly, i run 93 octane non-oxynegated gas, and i have replaced log style manifilds and the flappers for the exhaust . Still having the same problems. Finally last time i took it out we cruised around for a while stopped and i couldnt get it to move. It would run just fine until i put it into gear. We timed it while out on the lake but could only get it to run good around 12* bdc shold be around 8* bdc. checked the timing chain to see if it is stretched. 5*-6* of play in the timing chain. I read thats within tolerance. Right? The thing is i can turn the shaft of the distributorwith my fingers not much but a few degrees for sure. is that normal? Is that a mechanical advance that replaces a vaccum advance? Secondly if the mechanical fuel pump is bad will it always leak into that glass bowl? please help. and fast. summer is going by fast!!