The carbs probably got a float or valve problem, assuming the floats lever isnt bent (the thin tin finger in the middle that closes the valve as the float raises), its either its not sitting right on the pivot pin (check the pivot pin isnt bent & restricting movement) or the valves not closing, if it isnt then its probably got dirt in it or gummy petrol deposits if its been sitting for a long time. Its all quite simple, but make sure you take loads of pictures with your phone to remind you where everything goes if you arent used to them!). Theres also a possibility the return pipe to the tank is blocked.
Its hard to say what the lever problem is, or what parts broken. If its stiff its usually the vertical pivot seized, which sits on the back of the box, underneath, behind where the drivers side driveshaft comes out (its the pivot that one of the gear lever rods attach to).
Most of them have the nut welded on the top of the inner pivot pin, which can be carefully ground off (try not to wreck the thread), enabling you to dismantle it, clean it & then grease it.
The nylon cups at the end of the gear lever rods tend to break over time, they are cheap enough, about a tenner if you get the kit off ebay, but they are fiddly to fit.
Good luck with it!
