Hey Grumpy, The older engine is back together and I have had it running. It is missing the anti-oscillating spring but ran OK for me to tune it.
It is running as expected.
It had just a little "PUTT" from the exhaust every now and then.

So I am all finished, just have to source a few bits to complete them fully.
Once I do a bit more mowing with them, I will give them a tweak here and there and they will be two good mowers.

I have a spare base and will keep my ear to the ground for another GXV140 to do up.

I found these bases and engines good to work on. I like the way the bases come apart easily. Also the engines, I mainly used a 10mm socket and spanner.
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Happy is he who penetrates the mystery of things.