like a shotgun

Like in the movie Uncle Buck my landy shoots a afterfire? out the tailpipe about 4-10 seconds after I kill the ignition. Also if I don't put it in gear and use the clutch to lock the engine she will diesel for about 30 seconds and possibly backfire out the carb. hehe A real head turning display in the parking lots. lol

Can somebody explain which way how to turn the mixture down (clockwise or anticlockwise) what ever else could be the problem. Why is there unburnt fuel in the tail pipe? I have tinker with the settings already on the carb, but I am a little unsure which way to turn the mixture screw as the problem hasn't gone away and I don't want to run to lean. I am sure there is black carbon build up from a zenith warp problem a while back. The plugs are the correct kind now they are hot type, before there was cooler running spark plugs. (2.25L Petrol)

love uncle buck! If youve got a zenith, the mixture or volume screw is sticking out of the base of ghe carb, pointing at the offside headlight direction, ish.From scratch set the vol screw all the way in gently then back out 720 deg ( 2 turns) then start and warm the car up fully. Unscrew the screw to richen so revs rise then just start to fall. Adjust it in to get peak rpm. Then using the idle stop, get revs down to about 7 to 800 but lower is vetter if you can. Repeat the above again. You should be roughly there then
BUT before fiddling with the carb check static timing, valve lash and that your carb isnt warped or worn in throttle spindles etc....
Those backfires arent purely idle mix settings! I would rebuild the carb as a matter of servicing to ensure it is close to how it should be. Those zeniths csn be a pain in the ar$e.
forgot to say, dieseling is usually exacerbated by carbon deposits in combustion chamber. I dont recommend it but i have used seafoam on outboard engines as well as redex, both poured down carb choke. I wouldnt recommend it but it worked on 2 strokes! Proper way is head off and clean.