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Riddervold,It does not seem that friction is a problem. As others have said the timing could be off slightly, but another thing worries me a bit now after seeing the video. I am wondering if the piston diameter is large enough. On both my Duclos designed engine as well as the poppin, the ratio of the piston diameter to the cylinder OD is much larger....meaning that the cylinder walls are thinner. I don't know the limits of the design parameters required to get a flame licker to run, but I think you may be below the minimum as far as piston diameter.
Dont know where you reside if its in the UK meths is not the best fuel and its hygroscopic and that maybe the reason for the yellow flame.I use shellac thinnersGood luck