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.
Thanks Grumpy,
Good to see someone else feels the same way about that plastic carbie. I hope someone else can tell me what to do with it (apart from "shove it" that is !)
re: Your suggestions:
1) The muffler is clean - I checked this weekend - in fact I need a new one as it no longer seals to the engine - rusted away there so it is definitely not suffocating the engine.
2)Rings and bore should be O.K. I put new rings in 2 years ago and only used the mower a few times before this problem started - due to lack of time I put it in the back of the shed and only recently got it back out to fix. I will check them again this weekend though.
3) The fuel filter in the tank was removed by some previous owner and there is no blockage there - fuel gravitates from the pipe with no restriction.(I strain the fuel when filling the tank as I use one of those funnels with a built in strainer).
So I think that I can safely rule those 3 out but your other suggestions are good and I'll check those points next weekend.
You mention "
or air leakage into the inlet pipe (perhaps through a dislodged or misplaced vacuum hose". Please explain what you mean by "Inlet pipe" - are you referring to the fuel line hose or something inside the carby ?
Many thanks for taking the time to reply.
Jerry
