RE: What gas engine to replace an OS 1.60??
Somthing wrong in the Netherlands --
Having used that engine in 11 lb models (very light construction) - on pipes - we got pretty smooth low speed performance and a lot more power.
The new Roto's I am also running, do run smoother - I am of the opinion the ignition plays a role in this .
Send a memo to ZDZ or Amelung ( or where you purchased it) and ask if they feel your setup is correct.