Boy howdy did adjusting the float level and and adjusting the valves help! The engine really idles nicely now. I don't have a tach but I wouldn't be surprised if the idle RPM was ~900-1000. Also, the 'rich' exhaust smell is pretty much gone.
I hope your fuel problems are solved, but the grit in the bottom of the fuel bowl is worrisome. That means you might have a rusty/dirty fuel system. If you do, you are always going have problems with it. One little piece of grit gets under the float needle and holds the needle open a little bit, and the bowl starts overflowing with fuel. Then that piece of grit makes it through and everything settles down till you go over a bumpy road or something and dislodge more rust. That gets sent up to the carb and causes havoc again.
If you are using the original style fuel filter that screws into the carb, they usually have a spring loaded filter inside. When the filter gets clogged, the fuel pump pressure will push the filter back against the spring and bypass the filter. You might want to take your fuel filter off, get a clean paper towel and pour the filter out from the inlet, and tap it on the towel to see how much junk is in it. If it's full of rust flakes, I would look about getting a new fuel tank.
I would be a little more worried about the grit in the fuel bowl if it weren't for the following (and the fact that I could count the grit particles - there were four);
- I drained as much fuel out of the tank as I could back in July/August when I had the bed off of the frame. I believe there was only a gallon or two of fuel left in the tank and I found very little debris in the bottom of the catch container (no rust).
- I have been running a "pre" fuel filter, that's clear, just where the hard fuel line ends in the engine compartment (in the vicinity of the where the knock sensor was on the block). The filter has remained grit/rust free the entire time.
- I punched holes in the top carb gasket where the two 'air tubes' are in the air horn. And, the air cleaner assembly was off the truck for a few weeks (with the truck in the garage). The carb was covered with a rag but it would be easy for a bit of grit to enter the float bowl.
The screw-in fuel filter is new (which does not preclude it from being full of rust/grit). And, I will check it for debris as well. Right now, I'm thinking I'm just dealing with debris that entered during re-assembly and tuning.
While I had the top of the carb off, I noticed that the jets were 56F (F = Ford and H = Holley - also Holley jets are 1/4" thread while Ford jets are 5/16" - not interchangeable). It's also pretty clear, from the enlarged screwdriver slots, that the jets have been in/out quite a few times). Knowing nothing about how these carbs are jetted from the factory, I used Google to gain some knowledge. It seems that the 2150 1.21 Venturi carbs came with 56F jets. The 'smaller' 2150 1.08 carbs came with 47F jets. I am going to start using the spark plugs to determine if the jets need to be a little leaner.
That said, does anyone know which jets they're running in their 2150 1.08 carb?