Don't know what model of tiller your Tecumseh is fitted to, but this type of engine is usually filler to 'low-end' machines. The 'clutch' function on these is usually accomplished by moving the complete engine and mounting assembly relative to the rest of the tiller. It's usually mounted on 4 bolts that run in slots in the bodywork, and the drive belt is kept 'slack' by a couple of strong springs. When the clutch is pulled 'in', the engine assembly slides, and tightens the belt.
The point of all this is that the attachment you are looking for is probably nothing more complcated than a bolt/screw sticking out of the engine mounting plate.
phil_saunders(a)bigfoot.com
Phil Saunders, August 2012
