Melted plug extender on my '79 308

It might show these symptoms once in a while when idling, mostly upon start up on a cold motor. When giving it gas in neutral these symptoms definitely become more pronounced but for the most part it will take idle freely to red line. Once in gear with load is when the symptoms are at their worst to the point where the car will not rev over 5500.

It is definitely spitting and coughing through the carbs more than anything. Once in a while the cough and a spit is followed by a backfire through the exhaust. All of the above get exponentially worse when driving as opposed to idling. When checking the plugs, keep in mind that the most the car is driven is a couple miles here and there and several different sets of plugs have been tried, they definitely look like things are a little on the lean side.

From my research on F-chat though it seems like the idle jets at .55 should not be too lean, perhaps rich if anything, mind you I have a '79. The car runs well until it is past the idle stage progression of the Webers. It is not until 4000 or so before the problems start progressing until the car is not drivable over 5500. From what I have read the 220 air corrector that I have are definitely on the lean side of things, but I just have a hard time believing that they could keep the car from revving over 5500rpms.

 

The car should run just fine with the stock jetting, they did when new. My car ran very well with stock jetting after a complete cleaning and partial rebuild by a local mechanic (78 308GTS with 14k miles at the time). Only later did I start messing around and had the main jets increased to get rid of the lean operation designed into it....after removing cats of course.

 

Absolutely! At idle and under light load, the intake manifold pressure is low, and always a vacuum. But under load, and at higher rpm, intake pressure can reach to, and sometimes surpass atmospheric pressure. And as combustion pressure rises, so does resistance to current flow at the plug. Any breakdown in the ignition will show up at high speed under load and move to lower rpm as the problem progresses.

The burned extender is a sign of high resistance, most likely in the wires. A point ignition has a lower spark Voltage, but with the same overall energy in Watts at the plug. This means the Amperage are significantly higher, and as they generally have a longer spark duration, the wires take a greater beating than higher voltage systems. Make sure your wires have the proper resistance per foot, 400 ohms per foot IIRC, and check all insulators.

On the subject of advance, I modified a twin distriubutor into a dual ignition distributor, so the second set now resides at 135* to the primary set, and the second set fires the other bank, similar to a single distributor engine. The smoothness of both banks sharing the same advance has to be seen to be believed. Its like night and day.

When timing these engines, always set the timing at the high speed rpm setting (5000 rpm) and adjust the advance curve to "fix" the low speed/idle timing, or just live with it. But you can damage your engine if the high speed advance is out of range.

 

Thanks for setting this straight for me. One last question, I am going to take a timing light to the car over the weekend. This could sound stupid, but are there two different sets of timing marks on the flywheel for the front and rear bank? I am still a bit confused on how to set the timing on both distributors. If there is only one, from my searches here it appears that there might only be a TDC mark for 1-4, how do I set the timing on the 5-8 distributor?

 

Those curves look "pretty good"!!! LOL!

"Red" is always lagging behind though, did you correct it to get closer???

Take a look at this...
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What it means, I have no idea.......
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No, as you can see there are two sets of marks....

Wish I could help more but I really don't understand all this stuff!

 

Much appreciated. That is what I needed. I figured that there should be two different sets of marks but I could not find a definitive answer searching the forum.