Engine won't idle until it's warm (Ford 351W)?

I'll start by saying that this engine is in a boat. It's a Ford 351W and it has a 4bbl carb on it. It used to crank right up instantly and idle fine whether it was cold or warm. Now it takes a little gas to crank up every time. The biggest problem though is that it simply will not idle until it's had 5 minutes or so to warm up. If I adjust the idle so that it'll idle cold (500-600rpms), it'll idle around 1200-1300rpms once it warms up.

I've done a lot of work to this boat and engine lately so it's hard to pinpoint exactly what the cause could be but I haven't made any modifications and tune ups. I've changed the plugs with standard copper plugs (I know this isn't the problem b/c it ran good afterwards), replaced the exhaust manifold gaskets, valve cover gaskets, and cleaned up some wire connections that were done poorly by the previous owner. The electric choke still warms up and opens but if I let it open before the engine warms up, it makes the issue worse.

I'm kind of at a loss as to what could be the problem.