I have the Haynes carb manual for this thing and I was struggling to find the adjustment screws.
This is because certainly the mixture adjustment screw is very carefully hidden away to stop people dicking about with it. Yours may even have a tamper-proof plug over it, to stop you tampering with it.
So, here is the mixture adjustment screw, arrowed:
It’s a lot less obvious without the flash on the camera!
Just to help you find it, if the carb’s on the car then this is at the front of the carb, on the side of the engine bay where the intake trunking is.
Use this to control the fuel mixture at idle and normal running engine speeds. Turn anti-clockwise to enrich, clockwise to lean the mixture.
This is the idle control screw, arrowed:
This screw is easier to find, it’s at the front of the carb again, about halfway up it. I used a 9/32 1/4 drive socket to adjust it, but put my hand in the intake trunking side of the engine bay to get at it – there’s no throttle linkage that side! Use this to control the revs at idle.