[57Wayne]

1971 350SL, new to me. Fixed a number of little things and replaced tires. Took it for an inaugural run and noticed it would shut down, alternator light on immediately, and then restart, sometimes several seconds later with a good backfire out the exhaust (burning the unburnt fuel ).
Search of the site for intermittent ignition did not yield results. Any suggestions?
Ignition switch?
Thanks.

 

[57Wayne]

Found a 78 450sl cutting out discussion that will help. Tx

 

[dead battery guy]

I would start with the simple stuff first. check for corroded and or loose connections first.

 

[57Wayne]

Started at the distributor. Since I had some parts I removed from my cousin's 450SL for a Pertronix conversion, I swapped points, condenser and wire, and then swapped in her old coil. Have to go back and recheck point setting, but it ran much better today. Only when I turned into my street did it stall, and then it seemed associated with the directional being on, right or left. Tried it in the driveway (long driveway) and it cut out twice on application of directional. Then it went away. Would not repeat. Did not cut out. Hard to trace down that way!

 

[masand68]

Good start. Maybe the leftover parts from your cousins car are worn. Maybe consider converting yours to pert as well. That would take all those ignition parts out of the troubleshooting equation and even if not the final fix, still a worthwhile upgrade.

Also, it seems your problem affects all cylinders. I once had an intermittent short in the coil to distributor HT lead. It took a long time for me to find it, which I was finally able to diagnose in a dark garage. I could see the spark jumping to a nearby bolt. Might be worth a look.


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[57Wayne]

I've been looking at the Pertronix and plan to put one in, but need to find out if I need the 1885 or 1887 Ignitor. I find listings for both.

 

[masand68]

I've been looking at the Pertronix and plan to put one in, but need to find out if I need the 1885 or 1887 Ignitor. I find listings for both.

1885 works on our early cars. That’s the one I installed.


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[57Wayne]

Thanks for that info. What do you run for plugs? I have Bosch WR8DC+ now.
Also, plug wires; are Bremi good?

 

[masand68]

The cars came with 6K ohm, copper core wires and non resistor plugs. I’m running that config with NGK BP5ES plugs, can’t remember what brand of wire. But I do know other folks are running different combos that seem to work fine.

Spark plug opinions are kind of like oil opinions


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[57Wayne]

@masand68; how did you hook up the 1885 and did you use the Pertronix coil? I've done other cars but had no success here. I bought the Pertronix flamethrower coil "to make it easy".
Two ballast resistors, bypassed both, using the top of the aft resistor for a tie point of the two top wires since red had 12v in run position and lt blue went to + coil. Disconnected bottom wire on that side. Should have been 12v at the coil. Maybe battery was low but dropped under 10v at the coil when cranking. No firing. Not even a sputter.
I'd send a PM but haven't got that figured out either!
Thanks

 

[masand68]

@masand68; how did you hook up the 1885 and did you use the Pertronix coil? I've done other cars but had no success here. I bought the Pertronix flamethrower coil "to make it easy".
Two ballast resistors, bypassed both, using the top of the aft resistor for a tie point of the two top wires since red had 12v in run position and lt blue went to + coil. Disconnected bottom wire on that side. Should have been 12v at the coil. Maybe battery was low but dropped under 10v at the coil when cranking. No firing. Not even a sputter.
I'd send a PM but haven't got that figured out either!
Thanks

Follow the diagram here:

Pertronix Install with and without Switchgear

I was trying to help someone on another forum and it seems the hand drawn diagram (borrowed from Peachparts) we often use when bypassing the DJet switchgear causes some confusion. Radiotek has posted one too but it has the 12v supply from a less than ideal place. I pm'd Scott and he said he will...

www.benzworld.org

If you want to use the Flamethrower coil, follow the diagram that "Bypasses the Switchgear". In my case, I retained the switchgear (which also uses the original coil and resistors) which I think is an easier conversion and you don't need to deal with the tach signal.