Starting diameters

[Doc Brown]

Originally Posted by hannesd

no need for a chocke with a cold engine, indeed indicates a rich situation.
if it's obvouisly running rich on the bottom, i'd try the 40PJ anyway.
does turning the airscrew have effect with the 42 PJ? if not go ahead and put the 40 and be amazed
put on a closed helmet ,rain coat and pants an go out testride :-p

No, its too cold and too much rain at the mo.

But will give the 40PJ a try and report back. On Friday I'll measure the squish of the standard head, then replace it with a GP head and also measure squish with the GP head.

Yes, the air screw has an obvious effect with the 42 at least with my method to determine the PJ size. Currently it's at 1.75 turns but it was at 2 and 2.25 turns on all other Gassers I had (a 2018 and another 2019). None of my other bikes started without choke, not even when it was warm (25 C or 77 F).