This one was submitted by reader Paul Venne. Paul states that the bore and stroke are around 11 mm and 13 mm respectively, which would yield a displacement of 1.23 cc. The engine has a very early '50's Czech appearance to me, with a real AMA look about it, although no such engine is listed in Jiri Linka’s book of Czech model engines. The Czechs did make a fair number of odd-displacement models – this could be one of them. Note that the lower of the three radial mount lugs is missing, as is the needle valve assembly.
Can anyone put a name to this one? If so, please use the email link provided.