GMC.... You are exactly right, the main jet is too small, my mistake, not allowing enough fuel to return back to the tank. I ran an 800hp, 463SBC, with a terminator on it . My main jet of choice was an 85 with 39 nozzels. When I ran my backup 377SBC all I did was use a 33 nozzel and the same main jet. In my opinion the barrel vale should be between 25 & 30 percent. I feel like this guy had the barrel valve lean thinking it would take fuel away from the engine not knowing it would only lean it at an idle.