Resolved: Carbureted Chevy 350 ZZ4 Sudden High Idle

[The Mindless Philosopher]

Forum key word searches are coming up empty, so I'm opening a new thread.

My 2001 carbureted ZZ4 Boss Hoss started idling high this morning. Whether in park or idling in gear at a traffic signal, the idle has been around 1k RPM's instead of in the neighborhood of 650. The unit is a Carburetor Mike Stage II build with around 15k miles on it, give or take. Since it was running fine before I got caught up in a sandstorm a few days ago, I'll start by spritzing down the moving parts to make sure they're free of sand. I'll also check the vacuum hose(s) for leaks and the carburetor base to see whether one corner might have vibrated loose from every day riding. The sandstorm might have nothing to do with it, but the timing is suspicious. I'll also pull off the air cleaner to see whether sand might have somehow made it past the pre-filter bonnet. Fortunately, I re-routed the plumbing a few years back and rigged the tank for quick release, so accessing the carburetor and filter will take less than a minute. I'll follow-up with my findings.

[The Mindless Philosopher]

Issue resolved: it was a cracked rubber cap on an unused vacuum port on the front of the carburetor. I had a spare cap in a rebuild kit.