Join Date: Aug 2008
Location: CA, SF Bay Area
Re: GT390 Hesitation...
Great to hear it's solved!
The 4300 can be a fussy carb, they don't like dirt and the accel pump is very picky too so that was my guess as well.
If you had to ditch the kickdown on going to the Holley, check your auto shift points, they might be as much as 1000rpm lower now, unless you hold it in gear like I used to do.
If you like that Holley, you could either change throttle shafts or maybe adapt a "rat trap" throttle mechanism from an older big Ford 390 to work, then run the kickdown from the rat trap down to the trans. Most intakes have the two holes near the back to mount the rat trap assy.
BTW, as I gather it, you might officially have a 390 IP or "Improved Performance", not a 390gt. For 1969, the 390gt changed from a 600cfm Holley to the 600cfm Autolite 4300 and got a milder cam, to avoid needing a Thermactor pump perhaps.
Usually on an engine with stock iron exhaust and mufflers, I can get the Auto 4300 to cut times as good as a 600 Holley after a lot of fiddling, but a given engine might "like" a given year of Auto 4300 better than others. But hey if the weather is good, blast away with the Holley, they are a lot easier to tune.