After plenty of frustration trying to dial in my '76 carb, I pulled out a '72 455 carb that I had sitting in the garage. This carb made a huge improvement to how the engine ran. Still not perfect, but much better than the '76. Unfortunately, the '72 carb is lacking many of the vacuum ports that I need to get my emissions gear running. It also has very excessive clearance around the throttle shaft, which makes dialing in a "perfect" idle difficult. The '76 carb does have some play in the throttle shaft, not nearly as much as the '72, but I would still like to fix that. After reading the Doug Roe book, it looks like opening up the idle passage on the '76 would help me richen the mixture, since opening the needle valves as it is does nothing. In the book it states that pre-emissions (1970 and earlier) carbs has a .095" idle passage, and that starting in 1971, they went to .080" or smaller to discourage richening the mixture in the field. Since the motor idles pretty well at .080" with the '72, I was thinking that would be a good starting point to use when opening up the passages on the '76. I figure once I get the idle right, then I can address the other circuits in the carb. The gaskets on these old carbs seem pretty brittle and worn, I'm concerned that if I try to take one apart, I'll need gaskets, and they probably should be replaced anyways. Would buying a rebuild kit be a good way to get everything I need? If so, does anyone have a recommendation on a kit, or are they pretty much all the same? As far as a bushing kit to fix throttle shaft play, what's a good source for them? Thanks!
These carbs had their share of specialized passages. The off-idle is likely lean , as well as the jet and metering rod set-up. It is also possible that the '72 was intended for a big block, while the '76 was intended for a small block. This will have a completely different set-up, based on the breatihing capacity.
