I rebuilt the 390 for my 70 AMX, and on the dyno made 362 hp with an edelbrock carb. I then put on a newly rebuilt autolite carb that is OEM, and as I suspected, the hp was only 345. The problem was that the secondaries were sticking open on all the runs after that. We checked for sticking butterflies, but they were free. I heard from another AMC guy that there was a problem with this 4300 Autolite carb, and that "ponycars.com" , some Ford guys knew of a fix for it. Well, there are more than one Ponycars website, and can't seem to find anyone that knows of this "known problem". Years ago, with my original Autolite carb, I never had that problem. Has anyone heard of this, or did I get misinformation. Any Autolite gurus out there? Thanks in advance.