G,day cooper, long time no read,
You should be able to remove the rubber diaphragm from inside tap, and do the off mod. That is to remove the little tit on the plate with on/pri/res written on it and that will allow the tap handle to go up to the 12 oclock position and cut off the fuel flow. Some times you may be only able to get the tap to go to the 11 or 1 oclock position but thats ok the fuel flow will still stop
OR
Alternatively you could just use prime and the off mod but then you lose reserve, so option 1 is probly better
