Re: TR Carb tuning?
Your comment about the power circuit reminds me of a story. Seems like there must be a buncha 'jeep-type' folks that overlook a couple of characteristics of carbs, and either through ignorance, or from 'speed-shop' influences, they run with just about the opposite of what is needed for some off-road conditions. Obviously, you are correct about what happens to some folks, with the power-valve. I agree, if you are going to have a power circuit, it ought to be kept away (hg-wise) from where you are running. To compound the problem, the 'rock'-trip that I like to do, is at 6000-to-6500-ft elevation. This further complicates the power-circuit problem, because I really don't want the power-circuit dumping fuel right at the manifold pressure that the engine is trying to 'cruise' at.
The 'story'.... (This will likely convince some of you that I am 'nuts', as if you didn't already know.) Jeeps of the V6-era came with a Roch 2-bbl. I think it is called a '2-GC' (not sure). Stock, these vehicles have a reputation for running pretty poor in high-elevation, off-road, rocky situations. With stock gearing, it is common to spend an entire day slipping the clutch, loading up, stalling the engine, cussing, restarting, watch the exhaust belch black smoke, try to get going again, and repeat the process over/over. I've lived with a few of these vehicles, and learned to really not like the situation. So, on the last of these jeeps that I had, I started experimenting. I completely blocked off the power circuit. I found that the thread for the valve was standard, and I machined a fastener to fit. (BTW, the power valve lays in the bottom of the bowl, flooded in fuel, and engine vacuum is needed to close it off. So, every time the engine is started (no vacuum), there is a little belch of fuel, until the engine starts and creates vacuum.) Then, since these vehicles require so much bouncing in the rocks (wrong gearing), and the throttle-foot is mostly out-of-control, I reasoned that I didn't want the accelerator pump to work very good, if-at-all. So, I severly hampered the action of the pump, by finding an old leather pump in my junk pile, that was shrunk, and had a section that was turned-over. I nipped a little of the leather out, for good measure. It made a good 'bog', just like I hoped for. And, finally, without the benefit of any real 'science' or logic, I calculated how much smaller the main jets would have to be for running at 6000-ft. I think I remember it was something like .002 or .003-inch smaller. No testing involved, I just put in the smaller mains, and ran it. The results were as you might expect. It ran pretty awful at low elevation, and on the street. But, on the 6000-ft jeep trip, it actually worked pretty well.
So, what's the point? Aaron is correct. One needs less fuel, less power circuit, for some of the low-speed, off-road situations. (sigh... the benefits of FI sometimes look pretty good.)