I'm having a weird issue in where after the engine is up to normal operating temperature and is shut off for a short amount of time (10 minutes, or so), upon restarting it will idle fine but if I "blip" the throttle it will rev up to 3k and then slowly return back to normal idling speed. Sometimes the throttle doesn't make a difference and it just revs as soon as it starts.

It doesn't do it when started cold or when shut off and restarted within a minute or so or after a longer period of time. I've THOROUGHLY checked for vacuum leaks, adjusted the mixture correctly and set the timing to around 15 degrees BTDC. It does diesel a bit on shut down but I've found that to be common to some degree on higher compression engines.

The engine is a B20E .030 over, VV71 cam, ported head, etc. it's about 10.5:1 compression. I'm running dual SU HS6 carbs that are in good working order and fairly recently rebuilt.

I've scoured several forums on the issue and everything points to a vacuum leak which I haven't been able to identify on the manifold or carbs. Am I missing something obvious?

Any help is appreciated.