Hi

In the old day's there was plenty petrol engines that had a double
caburator , to switch between petrol and the heavier petrolium ( a
ligther sort of Diesel fuel ) .
For an old fasion 4 stroke slow running marine petrol engine, this also
work best, if the fuel are pre-heated, usealy by the petrolium tube
turned around the exhoust pipe , but also the air intake running thru
the exchoust pipe, help a lot pre-heating the more heavy fuel, when a
switch turn the gasolin chamber of the caburator to standby, and the
fuel was taken from the opposite chamber with petrolium.
------- the problems was the same ; the engine had to be started with
petrol on, but warm it ran well enough on the cheaper petrolium, and
the double caburator, made it so that only a switch needed to instantly
turn off the petrolium side so the engine would run more safe , say
when entering a harbour.