The stiff throttle is probably the grease dried in the cables.
Try this, take the throttle and brake assembly apart on the bars, get a tennis ball cut it in two. Pierce one in the centre and push it onto the throttle cable end. Fill will a tablespoon of oil and leave overnight with a rag around the other end of the outer cable where the inner cable exits. This will lube the cables.
The rough running is probably a result of dirt somewhere, either the carburettors, or the ignition system or it might even be muck in the fuel line coming form a rusted fuel tank. Check the fuel filter for dirt and replace if required. Check the points if its not electronic-ignition and clean with some paper between them.
The idle jet adjustment will be on the carb but it depends what carb as to exactly where it will be fitted. Take a look at this video on youtube. It's about a two stroke engine but where the carb is involved the mechanics will be the same or similar. If it's multi cylinder/multi carb then you will need to balance the jets to make it idle properly.
3 CARB SLOW JET ADJUST EASY WAY
×