flathead issues

[cosmo]

Blew the head gasket #4 on my 8BA engine with aluminum heads. Had antifreeze pouring out the exhaust. Replaced head gasket using copper, Used thread sealent on bolt threads retorqed to 50# all acrording to the book. Engine runs great now but when it comes down to idle alittle white exhaust starts coming out the tailpipe. I don't notice it when driving down the road, only at idle. Any ideas? Thanks, Dave