Thanks Gadge. And thanks for the really helpful links. Forgot to mention that the fuel tank has the name Morrison on it. The spec number in the Victa link of L1283 for a HK30 suggests that mine is also a HK30 with a spec number L1284. The link you gave has been the closest looking photo I've seen so far.
So I'm guessing I'm not going to find a new spring and will have to keep using what I have, or use trial and error with a new one. The old spring felt really loose so I, foolishly perhaps, shortened it by a around a quarter. It seems to run okay but I wonder if I'm not getting maximum revs now.
Thanks again. Ken
