If choking it consistently makes it run better, your problem is lean mixture, so making your test a few more times should show what the problem area is.
Lean mixture can only be: poor fuel feed (blocked in-tank filter, or fuel line); carburetor problem (I'll leave discussion of Victa plastic carburetor issues to one of the resident masochists); or air leakage into the inlet pipe (perhaps through a dislodged or misplaced vacuum hose) or crankcase (since it is a full-crank engine, this could mean one of the crankcase seals is leaking or has blown out of position). Realistically, it could also be a false indication caused by lack of compression (worn rings, scored piston, or faulty decompressor) or a blocked exhaust port or muffler.
You might check the crankcase seals: see that they are in correct position, there is no oil around them, and if you trickle a little fuel on them, it doesn't disappear into the crankcase. The other thing to try is remove the muffler, check that the piston isn't scored by looking at it through the exhaust port, check that the exhaust port isn't carboned up, and run the engine without the muffler to see if the problem still exists. Once you have made those checks there is no longer an excuse not to attack the devil's plaything, the plastic carburetor.
