It does go again!!!
If only I read the signs and stopped guessing at what was the problem. Remember I mentioned the problem with fuel running out the bottom muffler? Well that was the best clue I had to go by. I did everything within my power to ensure the magneto was right, dressed the contact points, gapped them and timed the magneto to the SPARK timing mark which as it happens is every revolution of the flywheel, no matter how many times you turn it over. I cleaned the spark plug thread out in the head just to make sure the plug made good contact but all of this made no difference to the no start problem. SO off comes the fuel tank and mixer. I grabbed the old gasket (fortunately still in one piece, just squashed flat) and placed it on the fuel tank, all good. Then I put the same gasket onto the fuel mixer, 'Hey Presto' found the problem. I did not remove what I thought was a piece of excess gasket that sat over the lip of the fuel tank. As it turns out, this is how the thing breaths in the air. It also explains the funny sounds early on about air rushing in and out of the mixer and up through the small hole in the mixture needle. I removed the excess bit of gasket and it sparked into life. I ran the engine for about 15 minutes and had no problems. I stopped and restarted the engine and again all good, and I did this a few times then no go again. So I spent the last couple of hours working this out. Again it was the new gasket. I bought a new sheet of 3mm cork gasket and made the new gasket with that just as the original one was. The problem this time was that the new cork gasket is not as good as the old stuff and had distorted a bit and swelled up a bit and may have been blocking off the area between the mixture needle and where the choke butterfly is. I simply cut that out and it is all systems go again.
I know from the past that cork gasket paper with what looks like rubber mixed in with it is no good with petrol so this is why I bought just a sheet of straight cork only gasket paper but it would seem that it too maybe no good. I will do another start up and run tomorrow and see how things go. All of this has made a real mess of the nice clean looking engine so a clean up is also on the agenda.
You can see below the pics of the gaskets the difference from What was needed and what I made.