Backfire when cold

Hi everyone, I'm after some advice as to why my 360 would start having the issue of backfiring through the exhaust when cold. Was fine for quite a while and developed this problem seemingly out of the blue, once it has run for a few minutes and starts to warm up it's fine. The other day i pulled the intake (tunnel ram) because I was convinced it had a vacuum leak, but it all looked good so I put it all back together with new gaskets and sealant. Did a compression test and that's fine, timing is fine, wires and plugs are fine. Distributor is a MSD ready to run, carbs are Edelbrock AVS 500 cfm (each). All parts have about 2000 miles on them. I'm starting to think its a carburetor issue, what do you guys think?
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