Replacement spark plugs after fitting a 123 system

[Dudlow]

Hi,   I have just had fitted a 123 electronic ignition system, with new coil etc. The instant improvement appears to be better starting and smoother running,  so all good.

My question is I have read conflicting notes about the spark plugs. Currently the car (67 250sl) is fitted with NGK BP7ES, gapped at 35. Can I expect any further improvement by changing the plugs or gap ?

Many thanks.

[cfm65@me.com]

Hi Dudlow,
Sorry I cant answer your question, but maybe you could answer mine. I also have a 67 250SL and purchased a 123 on my last visit to the UK. I have not fitted it yet but will soon.
Which model 123 did you install and on which setting.
Regards
Chris

[Alex D]

After a complete engine rebulid 2 years ago on my 250sl,  and installing a 123 ignition. For two years I was having major hot start issues and some cold start issues, but mainly hot start, even after turning the key, and pausing for a few seconds (up to 10 sec) in a few cases and still wouldn't start.  Even tried Chuck Taylors hot starting, "aid device" which in my case didn't help, but works well for some people.  Finally decided to put the orginial distributor back in, just to see what happens.  Immediately the hot start and cold start issues go away, now with the orginial distributor back in, no hot start or cold start issues for 3 months.  Maybe a bad 123 ignition?   Any one have similar issues with 123 ignition on a 250SL?

I have heard the following rumors, 250SL's are notiorious for hot start, more so than 230/280 and that 123 ignitions do not like hot starting to begin with, so the combination of a 250sl and having 123 igniton caused all my problems?   

[Benz Dr.]

I can't see why a 250 would be much different than a 230 given both use the same basic starting equipment.

[stickandrudderman]

Be aware that you should not use ballast resistors with 123 ignitions.
The instructions contain a table where you look up your original distributor number and it tells you what setting to use.
Be aware of the differences between throttle body types as some give vacuum advance and some retard. Plenty have been swapped over from original in both directions due to previous installer ignorance.
It's easy to check with a strobe that you have the right results and can just keep changing the setting until you find the right one if the recommended one doesn't give the result you need.

[cfm65@me.com]

TKS Colin,
Regards
Chris

[Dudlow]

Hi Dudlow,
Sorry I cant answer your question, but maybe you could answer mine. I also have a 67 250SL and purchased a 123 on my last visit to the UK. I have not fitted it yet but will soon.
Which model 123 did you install and on which setting.
Regards
Chris

Sorry Chris but the installation was supplied and fitted by my local garage and I'm not sure of the details.

On a general note we have no definitive replies 're the plugs.

[Benz Dr.]

Original Bosch plugs were W7DC which crosses over to NGK  BP7ES. If you go into any automotive store that's what they'll give you because that's what their book says. I believe that NGK BP5ES is your best choice for engines that are designed to run rich at idle. They're not too hot for mid range running so are basically doing two different jobs equally well.

[Atazman]

Do we change the spark plug gap after installing the 123 ignition? 

Someone earlier asked if hot starting was a problem with the 250 engine + 123 ignition.  That has not been the case for my 250 SL.

[Dudlow]

Do we change the spark plug gap after installing the 123 ignition? 

Someone earlier asked if hot starting was a problem with the 250 engine + 123 ignition.  That has not been the case for my 250 SL.

Atazman,   Its the same for me, huge improvement in hot starting which was getting progressively worse before the 123 installation.

Can I ask you which plugs you use please ?

[Atazman]

Hi Dudlow...............

I have the Ngk BP6ES plugs gapped at 0.035” with the 123 electronic distributor.  I gapped them at 0.032" before the 123 installation.  The plugs are always a good color and no misfires.

Just want to clarify in this note that I see no difference in my "hot starting" after installing the 123 ignition. Same as before the 123 installation, my car sometimes has a delay in starting after sitting for awhile when hot, but not what I consider a "hot starting" problem. Sorry to mislead you in thinking I have seen improvement.

[mauro12]

Hi guys, I have a similar problem because I want to change the spark plug and switch from Bosch to ngk. In the ngk website they show only the bp7es but i would like to try something hotter to avoid misfire. I also don’t understand why the pagoda tecnichal manual says not to use ngk (non resistor) but only resistor bosch. What do you think is the best plug for this car?

[66andBlue]

...I also don’t understand why the pagoda tecnichal manual says not to use ngk (non resistor) but only resistor bosch. What do you think is the best plug for this car?

Where did you read the info to use Bosch resistor plugs?? https://www.sl113.org/wiki/Electrical/SparkPlugs
That is not accurate. Whether it is Bosch, NGK or any other ones they should be non-resistor.

[Benz Dr.]

Alfred is correct. I use NGK  BP5ES and leave them at the factory setting of .032'' because most of the cars I look at still have the original ignition systems. 

[Shvegel]

Listen to Dan (BenzDr)  He has ignition knowledge and knows what he is talking about.

[mauro12]

If I change my plugs (bosch w7 I guess I have) and I But ngk bp5es or bp6es do you think I could have reduced co and better fuel economy due to the hotter plug ? Maybe bp5 is too hot? What do you think? I also have an electronic ignition.

[mdsalemi]

I have used NGK for many years. First I started with BP6ES. I believe they worked well. Then I switched to BP5ES, slightly hotter, upon the recommendation of Dan Caron. I think these work a bit better, they look cleaner upon inspection after some time.

Some anecdotes indicate that Bosch plugs "went downhill in quality" when manufacture was shifted from Germany to India.

I have opened up the gap to .035" based upon the recommendation of the Pertronix system with the Flamethrower II coil. They claim the higher voltage on the coil leads to a larger spark and the increase in gap from .032 to .035 allows a larger spark spread. Of course I can't say that's correct but am going upon recommendations. The coil does make 45kV while the stock Bosch is ~20kV.

I did get a bunch of BP5ES on a great deal and passed this deal on to some attendees at PUB this past September in VA.

[Benz Dr.]

My info from Bosch is the black ( standard ) coil is 13 KV and the red coil is 26 KV which is why you should use the 1.8 ohm ballast resistor in place of the .9 ohm. I would think that a slightly larger plug gap to .035'' would be OK with a hotter coil.