Yes that is the only thing I could see is supposedly 4 more cc's /// Looking at the replacement parts the 34 and 38 use the same piston, Cylinder and carb.... Not sure there is any difference except in the decals???
could be a case where the 34 uses the cylinder parts for the 38 if replaced. For example a Dolmar PS-6400 has a 64cc cylinder, but if you replace the cylinder assembly, it gets replaced with the cylinder assembly for the PS-7900