I've resolved the issue, it was a blocked muffler. I used brake clean, a block of timber to tap and an air compressor to blow it out and it now revs and runs like a dream. Plus, I'd set the float height on the original carbie but replaced it with another 3L carbie I had in nicer condition. I forgot to check float height on it. The float height was about 1.5-2mm too low but I wouldn't see that making so much of a difference.

OK, my mention of "crank seals as per compression readings", I had checked crank seals when checking the compression a few weeks back. Having an air compressor it's easy to do a leak down test via the plug hole to find anywhere air and fluids escape.

My frustration often means I don't properly express myself. Migraines, strong medication and age don't help.

The mower was starting hot or cold (after 2 weeks under my house)first click. Four winds, prime carbie, one click (Impulse starter), started and idled like a charm. It just wouldn't rev.

My condenser is 0.32uF (read with my multimeter) but they were being sold as early Victa 2 stroke condensers. Despite a difference to what was quoted it runs fine.
I knew the key-way and key were fine, I'd had the flywheel off a few times in the past week. The retaining nut is also sufficiently tightened,

I have a background in electronics and electrical (IT too) but spent the majority of my working life working in the mechanical industry as a mechanic and electro-mechanical specialist.

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Reason I ask is I was working on on a 2 stroke with a dead ignition module.i grabbed one that looked the same off a 4 stroke that was for parts,BUT would only start and run 50% at best.replaced it with a 2 stroke one and bingo.later hooked up the the four stroke module to a 4 stroke and it ran fine.

A 4 stroke ignition module would only fire half as many times as a 2 stroke module.

I am going to convert the mower to electronic module if just for the purpose of not having to remove the impulse starter pulleys bolt and the flywheel nut ever again. I'm having a heck of a time acquiring either, 1/2"BSF screws are like hens teeth and the 1" long stand off nut is as rare and impossible to chase up new.

Thanks for the assistance everyone!