308 with carbs keeps stalling after installing iridium plugs

I just switched to NGK number 6 iridium plugs and the car now suffers from running rough after getting up to temp, then stalls with backfire. It will start up again after a few minutes. And then eventually starts the process over again. this didn't happen with the standard number 6 heat range plugs, although it did seem to always run rich. Any thoughts?

 

How rich? What did the spark plugs look like on both the regular 6's and these new iridium 6's? Are the insulators tan, grey, black, or wet?

What about your spark plug extenders, how old are these? How do the ends (the ones that clip onto the spark plug) look? Do they grab onto the spark plugs tightly, or do they wiggle alot?

What spark plug wires do you have on the car and how old are these?

 

I just had my Mondial 3.2 in the local Ferrari dealer, where they observed I had Iridium plugs. One of the repairs they noted was that I should replace them with something closer to stock, since they said the 328 (and I assume 308) engines don't run well on them. Contrary to what I've read here, but just passing it along.

I couldn't tell that my car ran better r worse when I put them in, so I guess I'd look into other things first--i.e. are the extensions properly seated, wires on the correct plug, etc.

 

There should be no problem at all running a 308 and 328 with NGK EIX (iridium) plugs. With iridium plugs you should choose the heat range a bit colder, for the 308 the 8EIX would be correct.

Peter asked this already, how do your current EIX plugs look like?

 

I had nothing but problems with the iridium plugs in my 77. Changed back to regular NGK's and have had no problems since.

 

I run NGK 5ES in my 77 and after a carb tune they run just great. The carb cars all run a little rich on idle so I bet you are fouling out these plugs. For all around driving I have found the 5 heat range to be the best. I had tried 8's and then 6's before I saw some post about 5's. I could see the FI cars running with a colder plug but not in the carb engines. My 2 cents here

 

the plug wires when i first got my 308 were OEM, and had become so damn brittle over the years, that as soon as i started fooling with them i lost good spark. maybe you didnt get them all hooked back up positively, or you accidentally broke a wire connection somewhere (on the cap terminal or the plug end)?

 

why do you switch to expensive spark plugs, when then car runs o.k. with cheaper plugs ?
BTW; one day I got a brandnew set of Bosch spark plugs, installed them and two were faulty. Car began running rough and stuttering after being hot. Especially under hard acceleration-
Replaced them with the old ones. Problem solved. Next set was o.k.
Maybe you just have one or more faulty spark plugs.
It happens more often with spark plugs than one would think. Just one single jerk in the supply chain, who drops it onto a hard floor and ignores it, is sufficient to make problems.

Does your engine really stall completely or is it simply running rough ?

Best Regards from Germany

Martin

 

Unless you have a very high voltage ignition system, I would not run iridium plugs. Run non-resistor vanilla NGK BP6ES.

 

John, the fine tip of iridium or platinum plugs lowers the required voltage for the initial spark, so fine tip plugs are indeed very helpful for points and transistor ignitions.
With a high voltage CDI ignitions (Dinoplex, MSD) you don't really see a difference as the secondary voltage there is nearly double the amount of points or transistor ignitions.

 

This....and what are your gap????

The spec on the carbed 308GTB is pretty narrow.....I use .022.

The 'range" is .015 to .025.

Much narrower then the .035 "out of the box", so bang them on the concrete a few times.....

 

Great to hear all the input. I should've mentioned that this was a problem before the iridium plugs. But not as bad. The plugs were looking a little on the dark brown/black side the last time I checked. And will look into getting new extenders as mine do feel a little loose. The gap is too big so I'll change that as well.

When driving it last, it would get up to a certain temp (not too hot) and starts cutting out almost like a switch and looses at least half it's power. Then Bogs down bucks, backfires and dies. Maybe a coil?

 

Sure sounds like maybe a failing coil, I use the MSD High Vibration tolerant units as they are solid potted. They are specifically made for "any orientation in mounting"..

The OEM Ferrari ones are oil filled, and you really are not supposed to mount those horizontal (but of course every 308 in the world does)..it makes the oil run to one side obviously..

Extenders are either 'good' or 'bad", that doesn't sound like that would be your problem.

The thing to note is an excessive gap will act like a 'failing coil' as it is too large to bridge.
Just for fun go past my .022 "sweet spot" and try closer to the .015 - .020 and see how it acts.

 

Chocalate brown is as good as it gets in an unrebuilt early 308GTB.....

I use a '5' heat range to burn them clean too......not iridium...

 

In my experience they are talking out their hats. I have DR8EIXs in my 328 & it runs just fine on them. There are so many other components that can degrade before they fail in these ignition systems & because they are so expensive people (understandably) tend to make do till something actually breaks. There's a whole bunch of reasons one of these engines can run badly even with the best & brand new plugs in it.

 

Very interesting info on the coils. Thank you. I guess I should've mentioned that the motor is a fresh rebuild this spring. And one of the coils was replaced at that time with a used one that the shop had kicking around. I'll definitely look into the MSD coils after setting the gap correctly.

Thanks

 

I never had any luck with them on my personal car when I was running points. Same type symptoms which of course were gone once I changed to the standard plugs.

 

Yea, "used one kicking around" does not build confidence!!

Tho actually, I had a 'good used one" kicking around forever, for the exact reason probably, I put two matching NEW ones on the car!

 

A bad extender usually cracks/shorts to ground and stays that way, a continued misfire.

Good grief these beautiful machines have failed me at one time or another in every conceivable way.....

No wonder Amanda wants to trade 'hers' in, on a Saturn Sky....

 

The nice thing is that they are very close to fitting the OEM brackets, IIRC I wrapped a layer of 3M Non Corrosion tape around it to cover the awful MSD graphics, and off to the races...

 

My 2c worth .I fitted NGK iridiums to my GT4 about 5 or 6000 klms ago .Great, better starting ,less fussy around town,better fuel economy ,sounds crisper, can't really tell about outright performance.So I fitted a set to my V6 Mitsubishi 4wd,fuel injected ,electronic engine management.nothing ,zilch, no difference at all.So I figure more suited to multi carbs than FI cars.

 

Iain the FI engines run a lot different then the carb engines. If we don't run a hotter plug these carb motors tend to foul the plugs. Couple that with questionable wires or extenders and a set of points and a miss can be a bear to find.

 

In North America, it is standard practice to stay with NGKs in a 6 heat range. Some even use NGK 5. 7's and 8's seem to foul too easily in our driving conditions.

 

+1. I was always advised by some very experienced techs to stick with standard copper core NGK plugs, usually in the 6 heat range for a carb 308. I read once in Forza a tech suggesting NGK 5s. I would always use the coldest plug that doesn't foul...so try a 6 first.

 

Where exactly did you buy these from? Is there a certain type/model number?