1974 Mercedes 280 114 / 110 ignition timing

[Billy Joe Byars]

Please help me with the very best ignition timing for my car. I have a 1974 / 280 "North America" with carburettor. I have just installed "Pertronix Ingition" and the distributor is connected direct to carb with no emission control. This is my first post, and I thank you in advance for your help.

[t walgamuth]

so you know the total advance available for your car, including both vac and mechanical?

and does it have two vac connections on the dist.?

tom w

[Billy Joe Byars]

Hi Tom,

Thanks for the reply, I'm sorry to say that I don't know the amount of advance, but I do know that the advance works and that the distributor is the original. Also the distributor has only one vac connection.

Thanks again for your help.

BB

[Mike D]

The suggested timing setting is 4 degrees AFTER top dead center, vacuum line connected, idle speed 950 rpms, WITH vacuum being supplied at idle.

I set my timing ('73 280, automatic) with the diaphragm DISCONNECTED at 10 degrees BEFORE TDC. I usually plug the vacuum line and run it with no vacuum retard connected. This is because I converted from the Solex 4 BBL to an Autolite 2 BBL and I don't have all those Mickey Mouse vacuum solenoids hooked up. I hook up the diphragm every year at emissions testing but other than then I run on straight manual advance timing.

You can advance or retard the initial timing to meet your needs (for more "pep" advance it, for better mileage slightly "retard" it)

[Tristar1959]

Don't know how the Petronix is affected, but the book values for the stock transistorized US ignition for 73-74 in my M110 Service Manual, for the Bosch distributor 0 231 310 002 (check the little plate on the dist) are as follows:

with vacuum at idle: 4 deg After TDC (that's what it says)
without vacuum at 1500 rpm: 13-17 deg Before TDC
at 3000 rpm: 31-35 deg Before TDC
at 4500 rpm: 37-41 deg Before TDC (if you even want to turn those rpm's unloaded...maybe just hold momentarily to see where it goes, then back off)

The vacuum advance will add about 8-12 deg of advance through the range, varying on the rpm and the vac/centrifugal combo - say 10 or so for an average "add"; for instance - your 4500 rpm 37-41 becomes approx 45-53 with vacuum; your 3000 rpm check about 39-43 vs 31-35.

If you have the slightly later 75-76 Bosch 0 231 311 001, the corresponding values are: 7A/10-16B/26-33B/29-35B,
If the 76 Bosch 0 231 309 001 (unlikely - has both adv and ret diaphragms): TDC/11-17B/26-30B/26-30B(yes)

Dwell on a mechanical points version is 30-40 deg +/-3, transistorized
With old Coil, 39-42.

You may need to work those numbers back and forth against each other, to settle in the middle of the ranges, depending on how tired your distributor's springs are. If you get unstable results, check the fit of your vacuum line or renew it.

ONE MAJOR CAUTION with these transistorized ignitions systems, at least the stock - if the coil can't fire normally, it WILL find a path to ground, and will amplify the juice until it finds a path, even if it has to make its own out the side of the amp... (Check your Petronix literature for a similar caution)
DO NOT CRANK over without normal hot plug leads, OR if you must turn engine and don't want it to fire, either disconnect the supply to the system OR ground out the primary coil distributor lead, allowing it to discharge easily.
Stan

[t walgamuth]

i was going to offer some thoughts,'

but those guys said it so well.

tom w