My '74 450sl runs on 2 kinds of fuels, petrol and LPG (which is gas and very commen in the Neterlands in classic cars). It runs very bad on petrol, it has no power at all and runs very rough idle. I went to a specialized garage and they have replaced 2 injectors but that did not solve the problem. Another garage tells me that the valves are gone and that I am looking at a very expensive repair.
What I do not understand is that it is running fine on gas. When you use gas it does not use some parts of the engine like the fuel pump or injection but it is using the valves. Why would it run fine on gas when the valves are gone?

Best regards,

Jeroen