I've had these 2 stroke Victa mowers refuse to rev out when the exhaust port has mostly blocked up with carbon ,it's easily checked if that's the problem ,just remove the muffler and check the port hole isn't restricted, if it's restricted get the carbon out with a screw driver making sure not to damage the piston or rings in the process.
Also I would run the motor without the air filter element first, to see if it will rev out ,leave the filter housing connected and check it has a restriction hole in one end otherwise the motor won't run right all the Victa 2 stroke motors have a restriction on the filter housing ,then very carefully check the induction hose (rubber hose pipe) for any where the hose is not fully round as I've had a few that would not rev out because the air intake rubber pipe had slightly kinked on a bend etc and was restricting air flow and when I held the pipe with my fingers so the pipe is fully round again on the bends the motor revved out as normal.
An easy way to test this is to remove the air filter housing and put a straight short hose on the carby connected to the filter housing and run the motor or use kink free intake hose or straighten hold all the parts of the hose that look flattened , just hold the hose with fingers so it's round and unrestricted on all the bends etc when it's on full throttle .
I've had crank case bolts come loose and a crank case leak will stop the motor running properly, also check head bolts are tight and gaskets are good as a leaking gasket can stop a motor revving out.
You say that a shot of fuel down the intake pipe didn't help so sounds like the fuel tap is flowing fuel well enough and the needle in the carby isn't getting stuck shut. Sometime I like to turn the fuel off and just run the engine off a squirt of start ya bastard down the intake for a few seconds to see if the motor will run and rev out on starter fluid.
If the crank seals are leaking it will be hard to start and sometimes you can see the lower half of the crank will be wet.
