Carb chokin'????

ok I'm a lil new to older carb. engines and etc. so I need some help. I've got a 61 caddy original 390 with Carter AFB carb. and I'm having a problem. The engine will idle ok (maybe a lil high) while im in park or neutral but once I put it in gear and give it some gas it wants to die or it will idle real low. I've checked all of the vacuum lines so I dont think thats the issue. I am having problems with the manual choke but I'm not sure what it is. It seems like if the secondary butterfly plate is open a tad it idles pretty good but once its closed it wants to die and when its all the way open it wants to die. Whats my problem? Choke problem or maybe needs a rebuild? Maybe I should go with a newer edelbrock or holley? Which one if so? I need help, I wanna get this thing on the road soon. Thanks in advance...

 

First, report on what choke is actually doing: air cleaner off, engine cold, start and let it idle til warm. Choke should be closed with spring pressure apparent when you poke the plate open. Spring pressure closing it should be pretty light in fall weather, a bit more when it's real cold out. Choke closing should move a link to a widget on throttle area that holds idle up a bit--move stuff with your fingers before you start motor and check this out. The device won't actually affect idle till you move throttle (mash the pedal before starting) to allow the part to move.
As engine idles, choke plate should slowly open, and be securely open by the time engine is at normal temp. Again, the fast idle widget won't release till throttle is moved again.
If choke action is normal, next you enrich and then lean the mixture experimentally to see if either of those moves seems to improve the problem AND what speed range it affects.
To enrich, tie a wire to the choke linkage that allows you to close the choke incrementally as you test. If some level of choking improves things, engine needs more gas in problem range and that points toward actual problem diagnosis. If no good...
Lean the mix--pull off a vac hose or two to create a leak. Don't pull the distributor one--that will create ANOTHER reason for engine to stumble!
Improvement when secondaries are open you mention sounds like engine is too rich and extra air helps...

 

Edit--I see thing is converted to manual, so obviously do that drill manually! See if light choking at sart and then progressive opening of choke makes engine happy, or if less or more choke makes engine happier...

 

Thanks for the advice, I'll have to check when I get home. Does anybody know what aftermarket carb would bolt up and work good for this application if I choose to go that route?