Carburetor jetting won't cause this problem. It has almost nothing to do with idling (instead, adjust the idle mixture, choke and fast idle speed).

If the carb gasket is broken or leaking, it can cause this problem. Replacing the carb with a another carb (hitachi or weber) will "solve" the problem, but so will replacing the gasket.

I used a cork type gasket not sure whats it called but could this be causing the problem?
I made it myself just traced it from the original worn paper type gasket.

Use a paper gaskets, not cork. Rub both sides of paper gaskets with wheel bearing grease and use gaskets on top and bottom of insulation block.

An engine-quality cork gasket should be OK. To test, when the engine is running, spray WD-40 along the gasket join and if the engine slows down (or speeds up) you've found a leak. For more details, see Carb Troubleshooting.

Quote:On a Datsun 1200, you don't. There is no adjustment. You can adjust the fast idle, and the curb idle speed. But not the cable.

mine had the exact problem too...after top overhauling and changing to a new carb(old carb not original and leaking badly) the problem is gone. before that, nothing seems to fix it..now i dont even need to put my foot on the acclerator when i start no matter how cold or long i have left the car unstarted

i'm looking at a getting a new carby, mine has a cracked seal and apparently is a garbage carby anyway. saving my pennies for a weber down draft

tried spraying wd40 and also carb cleaner and the engine didnt run slower or faster
my engine runs great once after like few revs or holding the accelerator pedal for a minute or 2 on start up

In a serviceable carb, the first part of the [cable operated] choke motion moves a linkage that opent the throttle a little. This is the 'fast idle' function & is fully described in the workshop manual.
If the cable is pulled more, then the choke plate is drawn closed progressively to provide enrichment.

Normal idle speed is restored only when the choke knob is pushed fully in again. If this function, which is common to all standard production carburettors, is working normally on your carb, you need only pull the choke knob out a little way to give you the fast idle you need untill the engine warms up a little.

isn't another cause of running poorly when cold the dizzy timing?

seems like my B11 paddock basher idled terribly when cold, because the timing was too advanced and idle set slightly low.