Just an update
Running again.
The knob is a push fit. It is a pretty flexible plastic so you just wriggle back and forth and it pops off.
The o ring was hard so set about finding a replacement. Its a tiny bit bigger but victa fuel tap/ g3 main jet oring GA spares PTC807 fits and works as intended.
For anyone in the future struggling to start one of these, I have been trying different starting procedures. The best one currently is:
Push carby knob up (block main jet)
Prime 5x
Pull knob down
Prime 2x (squirt a bit of fuel in)
Choke on
Throttle a bit off idle
Pull cord and it fires first or second go and dies
Choke half and prime 2x more
then it will start and run mostly fine at half choke for a minute at idle.
Don't know if its the old diaphragm in the pump but it doesn't like being tilted at idle. Can tilt fine at throttle though. Must be fuel flow issue. Will change the tank filter and see how it goes
