Hi DCH:
We would love to have that engine back for us to take a look at. This vibration does not sound normal, but vibration is heavily dependent on the airframe and or mounting environment and therefore somewhat, in this sense, subjective. We have many , many of the 80's in users models and vibration is not a common problem. We will do what is required to make you happy with the engine, and if required we will refund your purchase price.
Please contact Mike Dooley at 301-374-2197 to discuss the next step
David Garrison
RC Showcase
ZDZ and RCS Gas Engines
www.rcshowcase.com