From the top
Your no idle problem is most likely the governor diaphragm
If you try to refit the cap with the center plug & spring in place the new thinner diaphragm will slip out of place so not make a seal
The simple check is to put a longer length of tube on the governor section of the carb then blow & suck
If the diaphram is working it will go faster when you blow & slower when you suck
When you fit the governor diaphragm, slip a LITTLE rubber grease around the end
Push the cap on strait till it clicks & double check it is home all the way round
Then slip the long spring in and the final cap .
Now for the hard bit
B &S discontinued all of the old Victa parts when they took over and AFAIK sent them all to be destroyed so there is no support for any Victa other than the new Briggs on a bowl model
However AllMowers list it
Victa slow pulley but they list a lot of stuff that they can not get to drag you to their web site and it is a pay first , then get told "we can't get it" 6 months latter situation.
The best source would be Bruce at
Outdoor King they do not list either the pulley or belt but he is genuine & knows mowers
Other than that you can just go to an engineering supply company and buy a M pulley blank
Stenco used to make an excellent range of aluminium pulleys although I have not bought one since before everything HAS to be imported from China
Pay the $ 5 and join the Outdoor King forum if you have no luck
There is a large number of very good old school tech on there who have a lot of old spares
Next best alternative would be to go to
Vintage Mowers which is an Australian based web forum ( this one is mostly US ) and has a dedicated Victa section plus there are a large number of Victa enthusiasts there who should be able to sort your problem out
It is also a PAY to join forum which prevents web bots & spammers from signing on so it is very safe & very helpful