Thanks everybody. I assumed one wouldn't push the thread back through the venturi, but thought I'd better check.
Floyd/Steve/Bill - I've come to appreciate the O.K. series engines. The 15 (or .149?) in question has the blunt ended O.K. needle which I find hard to set, - seems like 1/16 of a turn from cutting lean to cutting rich! It's about to be replaced with an O.S. 10 needle assy.
Power? On 10% nitro my Perky with this engine does an exact 60mph. A very civilised little beast. Done nicely in pseudo-U.S. trainer colours, e.g. wrong no. of red/white stripes on the fin. (Photo maybe when I get photos sorted).
A Rube? Can guess what it means. Did this with a kit Veron Combateer, fixed wheel u/c included, when we were testing the Rivers Arrow prototypes. We flew the rounds r.o.g. just to compound the image and lull the opposition into a false sense of security, and then surprised everybody, blasting our way right through to the final! By then it was a bag of torn tissue and I lost, but what a fun experience.
Good grief. Just realised we have two opinions, one says push threaded end, the other says the fuel end. Back to the dwg. board.