'71 280SL timing w/pertronix

[ryanpe56]

 The engine seems to operate much better w/o the vacuum advance hooked up. I set my timing to 30 degrees at 3000 rpm per the spec and it has an 1863 Pertronix kit on it in lieu of the points. If I hook up the vacuum adv. the engine shutters at 3500-4000 rpm. I see that the vacuum comes from an electric solenoid valve but I'm unsure of its operation.
Thoughts? Can I run the car w/o vacuum advance?  Also, I'm at 7000' and it operates at 8500' routinely.

[bracurrie]

I'll attempt an explanation of the solenoid switch and its affect on timing. Its a pollution control thing where a speed switch triggers the solenoid that uses vacuum to retard timing and under conditions like high engine temperature and/or RPM it blocks the vacuum which allows the distributor to advance all at once a number of degrees. There are posts here and a technical manual that explain it more thoroughly.
My engine has the same equipment, but the speed switch is malfunctioning so I disconnected the solenoid switch thus disabling the retardation. The idle RPM was then too high because under normal conditions the timing retardation lowers the RPM. Once I got the idle RPM adjusted down for no timing retardation the engine ran very well although I am not at the altitude you are running.
I've done a lot of reading and research about the evolution of distributor design for the M130 engine, but I am not an expert. As engine technology advanced after WW II, the optimal drivability and performance set up was a distributor that would advance distributor timing according to load and engine RPM. While at speed and the throttle at idle position the distributor would retard to save fuel.  In the late 1960s DB had to comply with reduced tailpipe emission standards but it had to do that while maintaining acceptable drivability and performance.
For me I would love to go to a setup from a 1968 M130 engine but that would require changing the fuel injection pump to get the full advantage of changing the distributor.
Brad
 

[rogerh113]

Hi,

I have a '66, and have been using a Pertronix for a couple of decades with no issues. 

The injection pump does have an 'aneroid compensator' which is in place to address elevation issues (I assume).  It is the short can shaped item on the top of the pump between the cold start assembly and the exiting fuel lines to the injectors. 

Since Mercedes were designed to operate in Germany, which has some pretty high elevations, they should not suffer at the elevations you drive at.  I do not know how to test the aneroid compensator, but it might be the source of your problem.  If you see the issue at high revs, then you might be placing demands on the engine without compensation for the thinner atmosphere.