When you pull the starter cord while looking at the gap between the spark plug electrodes, you should see an even string of blue sparks, and the sparks should not be thin and spindly.
You said you have scoring of the sides of the piston, when you look at it through the ports. That will be due to lubrication failure at some time in the mower's life. One way this can happen is due to blow-by (gas leakage past the piston rings from the combustion chamber) blasting the oil film off the cylinder walls, which normally means the piston rings are worn out and the engine has lost compression. It could also have been that someone ran the engine on straight petrol at some time, or it may have happened more slowly due to low quality oil, or insufficient oil, in the fuel. Victa specifies 25:1 petrol to oil. It is a good idea to do as they say unless you are sure you know more than they do. Note: Victa did get into a promotional deal with Valvoline in which they said they approved of 50:1 as long as you bought the oil from them with a Victa brand on the oil bottle. We don't know whether their engineering department signed off on that, or it was just the work of some genius in marketing.
Last edited by grumpy; 19/12/11 04:42 AM. Reason: Expand answer
