Re: Stiff throttle
Disconnect the cable from the carb and re-check. If it's still stiff, you have a cable or control box problem. Check that the carb throttle is smooth and free.
When diagnosing a problem, be it electrical, mechanical or hydraulic, the best starting point is to reduce the areas of investigation, usually by 'halving'. That is, put and imaginary line at the half way point in the system. Check each half. Now you should have one side without the fault and the other side with the fault. Do it again with the known faulty half. In 2 steps you have just reduced the area you have to look in to 25%!
The other most useful tool you have is your eyes and ears. Be alert to subtle symptoms. Also be aware of symptoms that rule a section/part out as NOT being faulty, just as useful as finding faulty parts...
Chris......