Hmmm. The idle speed should peak up to around 1000-1400 when cold and it settles down after about 2-3 minutes and idles at around 800 and about 650 in drive, but yours is a manual so there is no drive.
On the carb there is a cam which has steps and is adjusted by using a screw driver. Don't bother touching it unless the idle is way too high when cold starting.
I am just trying to think of things to check. Get some Inox or RP7 or WD40 and spray some in the spark plug-plugs, take off the distributor cap and spray a little around in there, put the cap back on and then take each plug off the cap and spray a little in the plugs and put them back on.
Another thing you can do for me is remove the air cleaner lid and filter. Yep, do it! Put down the bonnet lid and go for another drive. Don't worry, it will be fine as long as you won't be driving through a dusty desert. See if that does anything. Maybe go to the mechanics or call the RAA out and get them to use their timing gun and ask them to check it when idle. The timing should be set at 6 degrees before top dead centre. 6°BTDC.
Try that.