Hey everyone: I'm having an issue with the 1966 AFB on my 383. To begin, this is the original carburetor to the engine, and it is one of the early-style small pattern AFB carbs with NO COUNTERWEIGHT. It never had one. The issue is: the engine starts to starve for fuel when you stay in the secondaries any length of time. It does not bog, stumble, backfire engaging the secondary side. It opens up just fine, then after a couple seconds the engine starts backing off and surging. If I back out of it some, I can still partially stay in the 4bbl without it acting up. I've been into this carb at least twice. The first time I overhauled it since it had sat about 30 years unused. The second time, I opened it up to make sure the jets weren't swapped front to rear-they weren't. I rechecked the float adjustments and they were spot on. The secondary butterfly adjustment is also spot on. The only modifications I have done to the fuel system is a 1/4" spacer underneath because it kept percolating fuel in hot weather. Otherwise, the carb has all it's stock parts in it and the fuel system is brand new front to rear. The fuel pump is an offshore cheapo. I'm not sure what I could have missed, but I'm open to suggestions as always. Thanks!