Cost is about £2, takes 10 mins. Remove air filter. Unbolt entire tank/carb assy from engine (1 bolt at front of the tank, other (larger) bolt just in front of the filler. CAREFULLY unhook the throttle link as you go (you don't need to mess with the govenor spring(s)).
Separate the carb and tank (5 screws) Replace the diaphragm and gasket (both supplied in the kit), and re-assemble.
Takes almost as ling to type this as it does to do the job!
phil_saunders(a)bigfoot.com
Phil Saunders, June 2011
