The symptom you have described - cyclic variation in the speed of a governed engine - sounds like a common problem usually called "hunting". In the great majority of cases, the cause of hunting is lean mixture. Your Victa may have accumulated some crud in its fuel tank and it may be obstructing the filter they usually have in the tank, at the fuel outlet fitting. You will need to clean that filter if it has not been cleaned recently, and verify that fuel flows full-stream from the fuel pipe at the carburetor end, when it is disconnected.
Well I could have saved myself a lot of work!
Turned the tap on and the petrol just dripped out very slowly.
Removed the brown looking filter and it pours out.
Time to reassemble, fit a new plug and clean the filter! I'll update when it's back together and hopefully all will be well.
In an unrelated matter, the clearance between the two laminated steel poles of your ignition coil, and the flywheel, should be 0.010-0.012", which is the thickness of an ordinary visiting card. The amount of clearance, and it being equal on the two sides, is fairly important.
As someone else posted further down I was confused with the counterweight, when you said two sides I assume sides of the flywheel!
At least I have learnt a lot more about my mower now!
