1979 Mercedes 450SLC stood in a garage for many years and refusing to run and accelerate!
When it originally broke down a mechanic came and drained the fuel, cleaned out and replaced the fuel pump and filter and got the car running for a short time, but very roughly. It then stopped working again and was left in the garage for a further 10 years.
Another mechanic has visited recently, cleaned the system out, burnt the fuel pump out trying to rev the car and replaced it with a Mercedes pump. The car will start and ticks over, but very roughly and the fuel pump is noisy all the time. Any attempt to accelerate causes it to conk out immediately.
The following helpful suggestion from another forum has been tried but, disappointingly, was not successful
This may just be a stuck air flow plate/ fuel distributor plunger, common fault- the round silver plate in the induction plenum chamber moves up and down under varying loads and pushes a plunger up inside the fuel distributor, remove the dist block from its baseplate- do not dismantle this, just remove the 3 holding screws and turn this over in your hand. You will now see a shiny ball ended plunger that may well have stuck in place, remove gently without burring, clean in solvent and make sure it moves freely in and out. This was the most common cause of idle but no rpm and they would stick after a short time if they had been stood and plunger moved to a new position.
In my opinion (as a humble builder and not a car mechanic) the fuel pump is either struggling to pull fuel from the tank or failing to push it through to the engine. Has anyone please got any ideas on what might or might not be going on or going wrong?