I have both an SK 56 amd 90 (both ringed) and converted to diesel with Aj Coholics head. The same chinese engine maker also-appeared as Blue arrow engines also after useing the improvementss paul ordered as they are good and i have had no problems except a bad bad carb which was replaced under warranty. they are I think a little better than GMS and Tower
a good value. I have the JEN 56s and 47 all suoer runners no problems if bought under the JEN, SK or Blue arrow labels name tag
you should have no issues martin

The first ones out a few years ago I thought was not the best quality I would not buy a used one from that times period