Car: '85 fb with stock 12a and Nikki. No rats nest. Rb header. Emissions delete. Stock ignition system and fuel pump.

Problem: a few weeks ago I rebuilt my 12a. It went well and the engine now has 2k miles on it and fully broken in. It runs well to redline however there are a few issues.

1. At stop lights or any time the car idles, the idle will fluctuate between 800-1100 rpms. The rpms will sit steady and then the engine will kinda shutter and the rpms will dip, and climb back up it will do this every 1-2 seconds. After 2~3 minutes of idling it will forget to idle and just die. It Wil start back up again just fine though and will repeat this process.

2. Under heavy load but at constant rpm (going up a big hill) at around 3-4k rpm the car will again shutter/shake until either the load is decreased or the secondaries kick in and everything will smooth out.

It's classic vacuum leak symptoms but I literally have been looking for it for weeks now. I deleted the rats nest, sprayed a full bottle of carb cleaner everywhere (not all at once) trying to find the leak. Removed the carb and intake manifold twice now and inspected everything. The carb was rebuilt a week before the motor and was working well with zero issues before the motor was rebuilt.

Any ideas? Any hidden vacuum nipples or connections I might have overlooked during the rebuild...anything!?!? Lol

 

Brake booster? Sticky needle seats? Failing ignitor? Fluctuating / failing fuel pump? Crud in the fuel tank or filter? Clogged return line or charcoal can?