Seb,
Ok now we seem to be getting somewhere. I want you to look at the blade plate to see if you have any shine near the washer below the nut that holds the blade plate on.
If so you have not done the blade plate nut up tight enough or put the washer on incorrectly. The washer has NUT SIDE written on it.
The blade plate is your flywheel that balances the motor for the timing.
Also go to the Victa forum and look for topic on carby's and check your carby using the information.
See how you go with this first before we go any further.
Regards,
Bruce