Idle Issues

[canonball]

Disclaimer: Carbs are not my forte.

I'm slowly learning how to work on these things, I've got a '63 with original V6 and a brand new 2 barrel Holly that replaced the tired, old stromberg. At first it was running and idling great (last week), now the idle is throwing a tantrum. It's rough, doesn't want to stay running when it's cold, once the engine is proper warm it will usually stay running but it's still rough and periodically backfires up through the intake. But when the light turns green and you're giving it gas and moving through the gears it runs beautifully.

I'm going to take a look at it tomorrow and see if I can't figure out whats going on with it. My guess is either the idle mixture screws need to be adjusted or the idle jet might have debris clogging it up. The old fuel filter (I think it was original) was the little glass cup the fuel would flow through, not sure how well it filtered out debris since it didn't actually have a filter. Anyway, I was planning on getting an in-line I just haven't gotten there yet. But I figure with the old gas tank it would probably be pretty easy for something to float it's way into the carb and plug it up somewhere.

Given the issues, do those sound like feasible causes?