Rough Running Briggs & Stratton - Governer Spring to blame?

[Fatboy]

Hi Everyone,

I bought this old (circa 1970s from the B&S Engine serial if I've read it right) Haterette rough cut mower to deal with the massively overgrown garden at my new house, and while it certainly deals with ridiculously long grass, it does sound like it's not running quite right, and only really runs on a particular throttle position.

I'm not really familiar with these engines at all, so following some parts list and having a prod, I can see that the Governer spring appears to be a bit stretched -poking at the governer lever got it running at better than just an idle with no power, so it runs at about half power judging by the noise - I can make it run faster by pushing at the governer lever, but it won't stay and settles back to the lower power running, and the spring seems to catch on the pivot underneath it (see picture below with the air filer removed), I can find expanded parts diagrams but no assembly instructions or how it should be fitted pictures - any ideas what might be wrong - I got a new genuine B&S spring off Amazon (PN 261105 as best I can tell from parts catalogues), but it sits in the same way with the same issues - can anyone point out what I'm doing wrong or where to find some more information please?

[SystemOfAFrown]

Take the cowling off and check the governor vane pivot moves freely and the area around it isn't clogged up with old grass clippings.