Okay, had the day off today so I grabbed a spare junkyard carb and gave it a closer look. It seems that my current carb isn't releasing the high-idle cam, or at least I *think* that's what it's called. It's a small, claw-shaped bit on the back (firewall side) of the carb, directly behind the throttle linkage. The choke butterfly in the carb isn't budging from its near-vertical position.

The idle screw had no effect. Looking at the junker carb, there's a bunch of travel on that screw, but not that much effective adjustment distance. I've managed to get the idle down to around 1500 - 1600, but the truck still diesels for a good 45 seconds or so before it finally dies.

Can this situation be fixed without removing the carb? The junker carb is just that--it has so much guck on it, it looks like it's been dipped into a tar pit.

What should I try next?