Do you have a vacuum gauge to check idle vacuum and to check that it's steady also at idle, if so report back with that number?
Black smoke out the tail pipe is from excess fuel and if you see this emission while just driving on the Carbs primary side then it's not likely a secondary side issue, however there are a lot of things on the primary side of a Holley that can make for rich running above idle.
How is the fuel level at idle at the site plug?
I would start off with replacing the power valve if the fuel level is ok which is likely a 6.5" type an I would also do the metering block gasket.
You need to figure out what is making this condition pretty fast because seeing black smoke means the cylinders are getting washed out of the oil that they need ware at a normal rate.
Last but not least your timing chain could be ready to let go which can make for your condition in some respects.
pS, you can rotate your photos in your phone with the controls that appear when your looking at the photo you want to use.
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!
1) 1940s 100% silver 4 cup tea server set.
Two dry rotted 14 x 10 Micky Thompson slicks.
1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.
Education is what your left with once you forget things!
Last edited by steve25; 10-18-2021 at 11:41 AM.
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