What exactly does the devac DO? I read through this whole thread, and there seem to have been issues that were largely MASKED by the vacuum system (I think my vacuum system is CAUSING some of mine) but otherwise seems to simplify the whole engine.
You're exactly right. The main benefits are a ridiculously simplified engine bay, and the elimination of many points of failure.
In a "normal" devac, what sort of impact can I see on MPG and power? Are there downsides to doing this, and what are they? I know one wrote that it HURT his MPG, but it seems he had other issues that caused that.
MPG typically goes down a little due to the fact that the carb runs more rich. The emissions equipment watches for some different conditions that make the carb run more lean or rich depending on the situation, and that goes away. The changes are bad for performance, but good for emissions. The devac keeps the carb in its natural state of 'rich', which is what brings down MPG a little.
The two biggest downsides are that you absolutely cannot pass emissions inspection in states like California or anywhere that does a visual inspection. Sniffer-only tests can be passed, but it's harder. Pull out all the stops and tricks that are out there when you go in.
The other is that the car can be a little harder to cold start. The choke isn't working exactly as it's meant to along with the vacuum throttle control. Some people have trouble, but starting a carbed car is never as easy as a fuel injected car.
As long as you live in an area where it's legal to do so, it's definitely a good idea on a car with a problematic carb!