mercruiser 454 idle trouble

I have a 1981 mercruiser chevy 454 that does't seem to want to idle. I have only owned the boat a few weeks so I couldn't tell you the history on it. When I first looked at it, it didn't pump any water and the choke didn't work so I didn't run it long enough to warm it up, but it would run smooth at partial choke if I did it manualy so I figured everything would be good with some minor repairs. Well, the water pump issue is fixed, but the rough idle is not. I can see fuel being delivered through the carb with partial choke or at high idle, but once you unchoke it at low idle, the fuel stops coming out of the jets. I figured bad intake manifold gasket or plugged jets so I rebuilt the carb, figured it may need it anyway. That didn't help. Next I checked the vacuum, it says "late ign timming". I have adjusted the timming but it makes no difference.
Oh, I should also mention someone put an automotive HEI distributor in it at some point. When I went to adjust it based on my vacuum gage, I realized it was already loose.
I'm thinking maybe the timming chain may have jumped but I'd appreciate some other input before I start that project.