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  #1  
Old 06-26-2013, 01:48 PM
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w108 Dwell issue (?)

Hi,
My '69 280se m130 has a Pertronix 1864(?) ignitor 1 setup with the flame thrower coil. My timing is 30 degrees @3000rpm and 8 degrees at idle. But my dwell is only 20 degrees. I've had this setup for 8 months now. The car used to run great. For a week now, it stumbles under high RPM and/or high load conditions. My mechanic says my timing and mixture are fine. He thinks my dwell is the issue. The cap, rotor and ignition wires were also changed 8 months ago with the Pertronix conversion. I get more raw gas smell now with this stumbling issue so initially I suspected a rich condition that my mechanic denies is the case.

Pertronix claims that the dwell is fixed at 24 degrees and 20 sounds a little low. They also claim that all of these conversion kits from different manufacturers have about the same dwell.

I contacted hot spark and they claim their dwell is 40 degrees.

a) Do you guys think my dwell is too low? It ran fine for months with this dwell...
b) Can anyone confirm that the hot spark setup has 40 degrees of dwell?



Thanks,
Narayan

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  #2  
Old 06-27-2013, 02:28 PM
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Which distributor are you using? The 051 or the 062?
38 - 40 degress of dwell is normal - 20 degrees sounds kind of low to me.

Personally, I don't care much for those conversion kits. Some of them work OK and some of them don't.
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  #3  
Old 06-28-2013, 03:40 AM
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Quote:
Originally Posted by Benz Dr. View Post
Personally, I don't care much for those conversion kits. Some of them work OK and some of them don't.
Which begs the question, which ones?

Benz Dr's List:

Works OK:

Don't Work Ok:

I anticipate the reply with an open mind.
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  #4  
Old 06-28-2013, 09:56 AM
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Pertronix works better than a Crane system but that's not my close minded point.
I don't work for Pertronix, go ask them what's wrong with it........
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  #5  
Old 06-28-2013, 11:27 AM
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Quote:
Originally Posted by moby dick View Post
Pertronix claims that the dwell is fixed at 24 degrees and 20 sounds a little low.
a) Do you guys think my dwell is too low? It ran fine for months with this dwell...
I would think that with a Pertronix or any other points replacement, you get the dwell that the vendor chose to design in. So long as you use the kit they recommend for your particular engine, there should never be a dwell problem. The difference between 20 and 24 deg could just bean error in measurement. To be honest, I have never even thought of trying to measure Pert dwell using the old analogue meter I own.
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Old 06-28-2013, 12:51 PM
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First off. Don't try to compare the dwell of an electronic unit to a mechanical unit. An electronic unit will ALWAYS have a "shorter" dwell.


w108 Dwell issue (?)-dwellanglew2.jpg

When you set the dwell on a mechanical switching point set you are attempting to get an average for all contacting points. Wear and point bounce are calculated into the recommended settings. There is no bounce or variance in a Hall Effect or optical sensor (there might be a slight one in a variable reluctor system but that's a whole different affair). The Pertronix/Hot Spark set ups are Hall Effect systems. Any difference in the dwell between the two is merely a difference in the internal magnetic switch
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Old 06-29-2013, 01:38 AM
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Why don't you put the points back and see if it fixes the issue. It's pretty easy to 'un-convert' a Pertronix.
You may have to use the stock coil, tho, the Pertronix coil may be too 'hot' for the points and burn them up. Happened to me with another car, long time ago.

Csaba
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Old 06-29-2013, 10:06 AM
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To answer some of the questions above...
a) I have a 0 231 116 051 distributor.
b) I can't go back to points easily as I threw away everything I removed and I removed everything I could.

I have some parts on order. New cap and rotor, spark plugs and the hot spark ignition. Yesterday I swapped the coil to a new version of the exact same coil I have, pertronix 40511, and the problem improved by about 30-40%. After a 2 mile test drive, the coil was very warm. I could still keep my hand on it though. I run a 0.038" plug gap based on Pertronix's advice to go slightly wider than stock spec with their system. I'm planning on going back to spec. I did notice with the newer coil, my exhaust smelt less rich.
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Old 06-30-2013, 02:05 PM
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I got more parts in the mail...
1. New cap and rotor did not fix the issue.
2. Six new plugs gaped at 0.034" solved the problem.

The plugs that I removed had about 2000miles on them. They were actually gaped at 0.041" when I rechecked. 5 plugs looked great. Cylinder #4 had ash deposits. I believe this plug was mis-firing. This is not a pertronix or dwell issue. My hot spark setup arrives tomorrow, so I may switch just to see if I can feel any difference.

Thanks to all those who took the time to respond.
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  #10  
Old 07-06-2013, 04:16 AM
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Quote:
Originally Posted by moby dick View Post
2. Six new plugs gaped at 0.034" solved the problem.

The plugs that I removed had about 2000miles on them. They were actually gaped at 0.041" when I rechecked. 5 plugs looked great. Cylinder #4 had ash deposits. I believe this plug was mis-firing.
I spoke too soon! The misfire was much better, but didn't fully go away. Today I swapped in the Hotspark setup and now the problem is finally solved. It's night and day, after I set the timing correctly. I don't think the car ran this smoothly with the pertronix.

But, I had a glitch. After I swapped the hotspark for the pertronix, I assumed the timing was fine as I did not remove the distributor. WRONG! The sensor sits at the different position compared to pertronix!!!! My initial test drive was a disaster. Car seemed fine at first, but at 75mph, I had smoke coming of of the rear with any throttle. As I slowed down for the exit, I was pinging with even the slightest throttle. My timing was off by 20 degrees. I was over 25 degrees BTDC at idle! I am surprised the car ran at all. Did I just screw up my rod bearings or head gasket? I set my idle timing at 11 degrees BTDC which seems to run noticeably better than 8 degrees. I don't hear any pinging or see any more smoke.
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Old 07-06-2013, 11:10 AM
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I have a similar problem with my '67 230S. My miss is at low rpm under load. It clears up when the revs climb past 2500 rpm. I have a new Petronix system with their coil. Went through the Zeniths, new plug wires from M-B Classic, 2 sets of NGKs. Can't say if the car ran better on stock points since I swapped the Petronix in immediately when I purchased the car.

The fuel system is clean so maybe I should try a Hot-Spark setup?
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  #12  
Old 07-06-2013, 02:37 PM
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My M130 with webers got MUCH better when I had it tuned at a weber shop and had electronic ignition installed. Not terribly the same as your situation, and I don't have any settings or numbers to contribute. All I know is that the car runs well now. And that before the electronic ignition it was very difficult to set the dwell...
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  #13  
Old 07-07-2013, 08:29 PM
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I drove the car some more. My coolant is now cloudy. I think I might have blown my headgasket. On the plus side, the Hotspark setup runs a lot smoother than Pertronix ever did.

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