[SoCalCoupe]

Here’s where I’m at: I did an amateur rebuild on the carbs, but the same problems persist. I did manage to reduce some warpage using a file—carefully—but I now don’t think that was the core issue.


One thing I discovered: these carbs should have fuel bowl vents, but they don’t. I plan to fix that, and I think it could help with the hot start problem. I also added spacers that fit under the hood.

Idle speed and mixture are now adjusted pretty well. The car’s a 4-speed, so automatic transmission gear lever position isn’t a factor. In the driveway, everything seems fine—throttle response is good, idle is stable and blipping the throttle everything seems fine. But on test drives, when I push in the clutch, the engine often slows down and dies. If I try raising the idle speed to compensate, it holds a good idle in the driveway—but then during a test drive, it won't return to idle and just races at 1500–2000 RPM.


It’s maddening. I don’t think this is an ethanol issue. I suspect it’s a transition circuit problem caused by opening the throttle blades too far to achieve idle.
(Quick recap for those less familiar: a typical carb has five fuel metering circuits—idle, transition, cruise, power, and accelerator. The transition circuit bridges the idle and cruise circuits. It’s controlled by a slot in the venturi that gets progressively uncovered as the throttle blades open. If the blades are already too far open at idle, the transition circuit is compromised.)


I had a similar issue years ago with a Chevy running a low-vacuum, high-duration cam. The fix there was to drill small holes in the primary throttle plates to allow more air at idle without opening the blades too far. That kept the transition circuit working properly, and it worked great—but that was a modified engine, and I eventually sold the car (but regret it).


Now here’s the thing: I’ve run a bunch of AI queries on my Galaxie setup, and it keeps recommending the same fix—drill the throttle plates. But I’m hesitant. That fix made sense for a modified engine. This Galaxie is (supposedly) a stock 406 with a stock cam and stock carbs. I shouldn’t have to modify things like that. I can't say for sure the cam hasn't been changed at some point, but everything seems stock.


Any thoughts on how to pin down what’s causing the inconsistent idle return and/or stalling while driving?