I thought I should post here for anyone who is experiencing failure of a Victa 2-stroke to govern (revving too high at full throttle, so you need to control the revs manually by adjusting the throttle lever while mowing):
Before you buy and replace a diaphragm or O-rings, before you cut or change any carby springs, and certainly before you file or drill any plastic carby parts:
1. Attach a clean hose to the vacuum nozzle, where it emerges from the cowling around the engine cooling fans. This plastic nozzle normally has a short hose that runs to the carby and moves the diaphragm (and attached poppet valve) up and down to govern the engine at the correct speed. You need some tubing of the appropriate internal diameter (~5 mm). About 60 cm long is convenient.
2. Blow or suck on the tube. If no air passes through, there is a blockage, probably in the small hole that sits between the cowling and the cooling fans. If this hole gets blocked, the engine / fan can not create a vacuum in the hose to the carby, so it will not govern engine speed.
3. You can try to clear any blockage with compressed air, if you have it. Or you can try to clear it by poking a thin wire through the nozzle. It needs to be thin because the hole inside the cowling is small - less than 1 mm. Even then, you will need to line up the centre to ‘pot’ the hole. If this works, the thin wire will continue into the space between fan blades. Then you should withdraw the wire, re-attach the vacuum line to the carby, and try the mower.
4. If you can not clear the blockage as above, it is possible to remove the nozzle (Victa CR03727A) for cleaning, but you will have to remove the mower base plate and engine to replace it. Still a DIY job, but not so easy.
5. If there is no blockage, the carby diaphragm may by faulty or one of the O-rings may be leaking so the engine runs lean and fast. These things are covered in other posts. It is cheaper to run simple diagnostics before replacing parts. (eg: does the engine slow if you attach your clean hose to the carby vacuum port and suck on it? - if not inspect the carby diaphragm and reseat it carefully.)
This is a common fault that is easy to check and fix. For some reason (no parts to buy?) it is rarely mentioned. Some people just replace things then give up and run the throttle manually.
