Black smoke is almost always a fuel problem...seems like it is running rich or the choke needs adjusting. Run the primary jets all the in until it starts stumbing, then back them out about 1/2 turn, then check exhaust again. I'm sure others will give you a few more tips..this might help...good luck.
(STAY THIRSTY, MY FRIENDS).
1990 IROCZ28 convertible (SOLD)
2004 Silverado Z71 4x4
2008 Pontiac G8 GT
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