thank you guys for your answers.

Your right, I dont live in the States. But I love my canadian MB and I would be gratefull for any help anyone can give me to put back my very nice car on the road.

From the beginning, I know that it is, at the end, a fuel delivery problem meaning that the engine dont start because there is no gas comming to the carburator. Having a 560 SEC and a 420 parts car, I tried different things, but the problem is still there. When the gas is not comming to the engine, the fuel pump are not working. It look like they dont receive any electricity. When they do, the engine start.

I dont think it is the fuel pump relays because I replaced them using the one of my other working car but it didn't change a thing.

I'm not a mecanic, but I assume that the problem is comming from someting "electrical", a sensor, a switch, a relay...anything that is sending electrical current to the pumps...

Retroguybilly is mentionning "fuel distributor". I will have a look into that.

Any other suggestion will be welcome. I dont have acces to a good MB mecanic, so I am on my own on this.

Bests regards

Chris