I will keep a keen eye out here for your results ‘cos I am just a bit ahead of you in that I have completed mine but it’s not quite running yet.
I have spoken to Jan and he reckons the piezo system is not really very good and he uses a more conventional coil and contact breaker system. I have gone for the Hall Effect electronic system and that works very well indeed. I drilled a hole in the outer edge of the cam in which to fit the magnet and fabricated a sensor holder in the base of the engine, this system of course does away with any extra mechanical drag on the engine.
I find that timing to around 20-degrees before tdc seems to work best. Also adjust the throttle lever on the vapour carb very slowly as it seems quite critical, best position seems to be nearly closed but with the air hole just appearing. I tried turning over with a pull cord, not enough. Use Jan’s method of using a rubber belt or band on the crank pulley and driving with an electric drill, this turns it over for much longer and gives a chance to position the throttle. Try other timing positions and keep notes of them and any results so you can refer back.
At the moment I can get it to fire quite well, sometimes flames coming out the exhaust! but I havn’t yet got it to continue running under its own power. Pay particular attention to friction, it should spin over very freely with the plug out and the fuel feed pipe disconnected. There should be a reasonable compression when these two are replaced. My plug gap is about 20-thou and I have modified my cylinder head to take a 10mm NGK plug although Jan’s plug also works well. Do be sure the non-return valve system is working correctly, blowing and sucking into the various ports will determine that. Make sure that at bottom dead centre your piston is as low as it can be in the cylinder without bottoming out, adjust this with the piston to con rod fork with locking nut, this is important as it provides suitable back pressure for the expansion chamber.
Those are my findings so far and I offer these in the hope that they may be useful, once you can get it to cough you have something to work on so – good luck
All the best, John