I just had another look at this LPG mower and why the new carby wouldn't work well on LPG.
I didn't spend much time on it fixing the problem ,just drilled the gas fitting out a couple sizes larger and put an angled edge on the brass inside of the carby also I had to change the throttle shaft as before I hadn't noticed where the carby linkage fits in is slightly different on the gas carby as it was for horizontal shaft motor and I'm using the vertical shaft motor.
One extra thing I did was install a plastic fuel tap on the petrol fuel line.
Turned the bottle on and it ran well but had to adjust the lpg down so the fitting most likely is drawing LPG better now.
It ran well on petrol too, no problems on either fuel.
Instead of using the alloy fuel bowl, I've installed a metal one.
