Rubber fuel line coming from pre-filter to lift pump can break down around fitting onto lift pump drawing too much air to keep the machine running at idle

Hi i work on these all the time, first replace all the rubber furrells on steel lines.
if no joy check the pipe to the lift pump off they come loose or block.
check the fuel line between the lift pump and the filter on the back of the tank.
they collapse.
1 of these i had was a 312 lc and could not crack it, so i changed all steel lines and lift pump which cured it. get back to me on how u get on