Ognyan,
Did you bond the tungsten slug in place?
Dave
Well, some details about pressing the tungsten slug in place. I had already removed some material from behind the crankpin; this turned out not enough to balance the engine, (measurements, calculations , etc.), so a 4.0 mm thick tungsten rod obtained, green marked. A hole / orifice was drilled on a coordinate milling machine with a carbide tipped drill bit. At slow speed of rotation. At the desired place. The crankshaft counter weight about 8 mm thick as far as I remember, so this was the length of the orifice. A bit longer piece cut off from the tungsten rod obtained , using an angle grinder. The tungsten piece became red hot while cutting. The two ends ground both to parallel. Chamfers provided. Then precise measuring tools at a friend of mine showed orifice diameter obtained 3.92 mm; the tungsten slug 4.00 mm. Same friend provided a thin enough round file covered with fine diamond powder. By filing and frequent measrements the orifice in the hard counterweight, the orifice diameter obtained 3.98 mm . At this point , the crankshaft heated a bit, about 60 degrees centigrade - this is what a human hand may handle most - the tungsten bit/slug pressed in the orifice, using a vise. The exessive length of the tungsten slug/bit, what was exceeding the 8 mm length, sanded away. Both sides of the counterweight. Until no tungsten protruding. No glue used. I hope the said/stated up to now to be enough. About the engine, it seem to run OK, rich settings available.
In case any other/further question, I reply to the best of my knowledge. Else, I have got another same engine that needs balancing too. Broken in but not in use. Aviastar 61 ABC engine seems to provide a bit more power than an Enya 61 CX (ringed.). I have got this too. Only that the Enya comes balanced, ready to break in and use.