I have a 72 240z completely stock. Car runs great throughout RPMs very strong! Once Ive driven around and temp is warm at a complete stop it idles around 1.5k and won't drop down. Also once I turn the key off pull out the key the engine remains on for about 5-8 seconds until it burns of the remaining fuel. First carb car any suggestions to fix this problem. Thanks for the help!

One common cause of dieseling in the 240Z is the electrical system backfeeding through the ignition. I had that happen when I converted the alternator to an internally regulated alternator. If that is the cause of your dieseling, a diode properly oriented in the alternator circuit will end that problem. Details can be found here.

As for your idle issue, are you choking the car when you start it? Have you checked to see if the choke cables are moving the choke or if they are bound? Are you sure you have stock carburetors? If so, search online on tuning SU carburetors, or contact Bruce Palmer, a member here, about buying a copy of the Z Therapy video on working with your SU carbs.

Whatever you do, stop that dieseling ASAP or you will break the top ring lands off the pistons and you will be an unhappy camper. Carbon build up, timing too advanced. Turn the car off in gear with one foot on the brake and let the clutch out...... That'll stop the run on......

Check to make sure your choke cables have some slack in them when the choke is off and make sure the nozzles are returning to the full up position when the choke lever is off.