a mech question on a non Mopar car ( pinging, mercedes 1975 )

[Nacho-RT74]

lets see... I'm having a big pinging problem with my parents 1975 Mercedes 280S ( W116 M110 )

I'm driving giving gas ( no matter the speed ), then pinging begins, change from D to 2nd, same speed, more RPMs and pinging goes away. Of course this is really noticeable with load, such as going up a hill because the pinging begings earlier.

I'm toward to mixture, but I have to check the vacuum hoses routes. The dist have double action vacuum, two hoses, one advances the other retards. Dunno the second one really goes on engine.

Solex 4x1 carb, which still I have to learn about.

[rt green]

what is the quality of fuel you are using?

[Nacho-RT74]

good question! 95 oct. but quality, unknown at this moment.

[Nacho-RT74]

( note, my Charger also pings at certain moments of throttle opening, I think when rears begings to open )

[Paul G]

Some things to check.
worn out distributer allowing too much spark advance
Gummed up distributer not allowing advance mechanism to return to normal state
carbon deposits in combustion chamber, pre-ignition is the result

I would go over the distributer and make sure the timing is correct

Use a cleaner additive in the fuel to remove carbon deposits. I have poured Techron, or Marvel Mystery oil, or another brand of fuel system cleaner directly in through the carb, in a warmed up engine, not hot. Pour it in until the engine dies out. Let it set for 30 minutes, then restart the engine and smoke out the neighborhood as the engine runs. It will smoke for a few minutes after restart.

[Nacho-RT74]

head replaced 2 weeks ago, but pinging has been now and then.

Dist worn! something to check definitelly!

its a points dist by the way

[Cooter]

EGR system not functioning. Also, timing belt/chain worn. Lemme guess, 300k miles and 'haven't had to do noyhing to it'?

[Paul G]

Head replaced. Did that increase the compression ratio? If the head was milled, or thinner head gasket used, that will increase compression ratio. Higher compression will be more prone to spark knock. May have to retard timing a little to cure that. Do the pistons have any carbon buildup on them? That can cause pre-ignition as well. 

[Nacho-RT74]

Head just resurfaced, stock headgasket. Pistons got regular carbon layer, nothing major.

the timming chain gets a autoset tensioner... it can be some stretched but the tensioner will set it. It's a DOHC engine