Timing, idle to fast, fuel mixture to rich, must likely one of these. Happens all the time in my Mrs Mazda, the engine has done around 400,000km's its loose and likes to run on, older engines tend to do it more than new ones.
thermocrap is meant to have a solenoid that shuts the carby off completely when you turn it off. ( this all assuming its a thermoquad of course ) so it will pay to check that.
If it's not, as has been said..timing. My XB used to diesel a bit with closed chamber 4vs and a Holley DP on it .. the hotter it was the longer it took to shut down.
yeah, but sometimes the solenoids dont work, so people just wind the screw in to make them idle.
Sometimes the shafts wear, and they such air in from there, causing them to idle lean and run on,
Possibly a spacer / heat insulator may help also, alternatively it may also be a leaky manifold gasket too.
Also check the oil, if the fuel pump is leaking, it may be running on fuel vapour in the sump, maybe the vacuum advance is connected to the wrong vacuum port? there is a number of posibilities
What is the idle rpm? does it sound like its idling too fast?
went and got a kit for it, now the car, no matter how hard we drive it, wont go over 1/4, or 1/2 with 1 thermo going..
goes better now, than when it was in the xb, or ute.... muffler, dejet the carby, and yeh... thats it....