erm,,,,, the bits i mostly fiddled with (on the disco..) were,,
there are two large bore pipes, coming off the carbs and joining into a Y piece then going into one pipe...(does this make any sense..??)
Think they are water pipes..?? Anyhoo... on the Y piece is a knob with a spring underneath. I think it does 'something'... Mixture maybe..??? I found this to be wound right in, so backed it off and lo-and-behold..... GAS POWER....
If anybody has a more technical explanation, it would be most welcome..