340 Chugging instead of Reving

Open headers can lean the mixture. Try going up two jet sizes.
The jets are currently 72. It was a size I chose to start with. The plugs read that it's running rich. Black and wet. When I removed all the plugs during a compression test, fuel sprayed out of the plug holes the first few cranks. I brought the rpms up to the break up point and shut off the fuel pump. It popped until it ran out of fuel.