Vacuum leaks
“Vacuum leaks. Very dangerous. You go first.”
Set the timing on the Spitfire last night. Instead of a nice 10° BDTC (Before Top Dead Center), it was somewhere around 22°. That calmed the idle down somewhat. However, it still wanted to stick around 1500 RPMs, and not very cleanly. Messed with the mixture adjustment (which in hindsight probably wasn’t the smartest thing in the world to do), and it still runs really rich.
Gave up, started putting the tools back in the chest and cleaning up, when inspiration hits. Vacuum leaks. You never checked for vacuum leaks.
Re-started the Spit, grabbed the can of starting fluid, and sprayed potential candidates for leaks.
Aha! One of the capped off emissions lines on the carb, when sprayed, causes the RPMs to increase. Looks like the rubber cap has deterioriated over time.
Add it to the list of things to buy at Auto Zone tomorrow.
