For Palm Readers and Spark Plug readers

[Don Coatney]

Hot plug, cold plug

[james49ply]

I notice that you have a vacuum line from where the single carb setup would be, the center plugs appear to be running lean, with the rear two running a tad rich. #1 looks good #2 ok, #3&4 lean, 5&6 rich. check to see if you have a vacuum leak at the manifold, the block over the center, or along the line to what I assume is the vacuum line to the wipers. just my thoughts.

[Don Coatney]

I notice that you have a vacuum line from where the single carb setup would be, the center plugs appear to be running lean, with the rear two running a tad rich. #1 looks good #2 ok, #3&4 lean, 5&6 rich. check to see if you have a vacuum leak at the manifold, the block over the center, or along the line to what I assume is the vacuum line to the wipers. just my thoughts.

I think you are looking at the picture of my engine not the engine in question owned by jd52cranbrook

[jd52cranbrook]

This is my current engine set up.

To me, the first four plugs look pretty much the same. I will check for leaks though, I will have more time over the holiday to look. Plus I am still tweaking the friggen fuel level sender to get accuate.

[48Dodger]

150 and 155 compression? that' a strong number. Is that wet or dry? I would consider closing the gaps and running colder plugs. If your not burning a lot of oil, I would think maybe the advance is too much. My real thought is this: the wide gaps take more voltage....#1 has an ash look (to hot: ie sucking up the current) and the last plug looks like its getting the "hind teet" on the distributor. Progressively the plugs go from a "hot" read to a "worn" read. Maybe your ignition system is having trouble dealing with the voltage needs in the current set-up. A plug with a wide gap, and can't get the voltage it needs under a load, will cause missfires. Just thinking out loud.

48D

[P-12 Tommy]

I agree with Don on the plug gaps. They just look too wide.

[jd52cranbrook]

150 and 155 compression? that' a strong number. Is that wet or dry? I would consider closing the gaps and running colder plugs. If your not burning a lot of oil, I would think maybe the advance is too much. My real thought is this: the wide gaps take more voltage....#1 has an ash look (to hot: ie sucking up the current) and the last plug looks like its getting the "hind teet" on the distributor. Progressively the plugs go from a "hot" read to a "worn" read. Maybe your ignition system is having trouble dealing with the voltage needs in the current set-up. A plug with a wide gap, and can't get the voltage it needs under a load, will cause missfires. Just thinking out loud.

48D

That's a dry compression number. Was getting 10 lbs more with the finned head, but it had been surfaced once.

I am running Langdon's HEI distributor. He gaps calls for 60-80. I have tried anywhere from 40-80, with same results.

I'm going to start with lowering the gaps to 40, and put the two 308's in 5 and 6 hole, and see whats up after a few drives.

All the information I get on the plug web sites is my two rear plugs are they are running rich. Either get a hotter plug, or adjust the carb. Being this is 2 X 2 set up, also from Langdon, and the intakes is not cylinder specific, I would think if the carb is rich it would show on other plugs.

This weekend I will check the carb out, even swap it maybe, but I bet it won't change the outcome.

I have already set the advance back to 4 a few days ago.

The pictures may not show it real well, but plugs 1 through 4 are actually very equal, and actually healthy. 5-6 show carbon build up.

[Don Coatney]

I am running Langdon's HEI distributor.

What does the engineer Tom Langdon have to say about this? He told me that nobody on the internet knows anything but he (being an engineer) knows everything. If you have not done so yet contact him and post his thoughts.

[jd52cranbrook]

I'll see what I can do.

[martybose]

If I was to hazard a guess, I'd look at the rear leg of the intake manifold. Think about it a minute; both of the back cylinders share the same intake port.

Marty

[greg g]

Also thinking out loud. If there are air leaks at the front of the manifold and you have compensated by adjusting the mixture on the front carb, and the rear is nice and tight, those two cylinders would be getting an artificially rich mix, while the other are working in what would be a lean mix if the carbs was reset to "normal".

Have you done he unlit propane thing on the front cylinders??? What happens if you put the fouled plugs in 1,2 and the clean ones in 5,6 and run it a while.

[jd52cranbrook]

Driving the car on freeway, about 65, rpms about 2,200. Gave it gas and got a misfire like before. Well, to me it sounds more like the carburetor is coughing, but that's just me. It coughs, momentary lack of power, like a miss. But no backfire that I can hear. Happened maybe a total of five times in about 3 minute period. Then ran fine, or no coughing at least.

Drove it home, pulled the plugs, number two plug has a missing electrode.

Sorry, cannot get a better focus.

But it is the same as the original problem. I did say before it was hole number three I think, but I could be wrong as that time I was not paying enough attention and very well could have been mistaken. Anyway, this time for sure its number two cylinder.

This is something I have never seen before. Would really appreciate some direction, or advice. Meanwhile I will go back to plug readings and see what I can dig up.

Don, I don't want to rehash the bad choice of words, or even a bad customer service manner with Langdon. He definitely has his own way. But I have read a lot of the early hot roding of inlines. He was definitely in the mix. I will, if I can reach him, find out what I can, but being the holiday he is probably traveling to a show to sell his wares.

What is really frustrating now, is I cannot find the original damaged plug. This one burnt looks very much like the first in the pictures. But I cannot fathom making that big of blunder and put it back in. I would like to think I am smarter than that, seriously.

As for plugs 5 & 6, 5 looks more like the other four now. I have about 200 miles since i reinstalled the plugs. And really looking at these plugs, they are black, they never were coated with grime or excess carbon like the samples show on the plug web sites. And look for that other dammed plug.

I guess it's very hard to compare to pictures.

Greg, I did swap them out, and after I would guess 200 miles or so to recheck they would come back the same, and the originally black ones would look ashen like the rest.

I have not done the propane test as yet, that is a option.

Marty, I realize the back two plugs share the same intake port. But I am reluctant to start taking things apart that have run well for over 10,000 miles at the least. I want to try a bit of logic first, and look at external items first. Although, my logic could be shot if I really did reinstall the damaged plug.

So I am back to the original problem of why the electrode burnt up.

[jd52cranbrook]

Also,

Did a compression check with the engine not quite cooled all the way down, a bit warm.

150 to 152 in plugs 1-5, with number 6 reading 156

[greg g]

What head are you running?? Is the reach of the plugs correct for the head???

[jd52cranbrook]

I am running the stock head. I am using 306's at the moment. 303, 306,and 308 are all 3/8 reach.

[greg g]

Were it me I would go back to the stock ignition set up, and try some AC 45/6's.

[jd52cranbrook]

I appreciate that, but I have run over 30,000 miles on this HEI set up. I don't think I have a stock distributor anymore. I do have another HEI one though. But it's the coil that provides the oomph,, right?

On a positive note, at least for my sanity. After talking with my partner in crime, we figured out I did not put back the original bad plug.

Those AC plugs, colder?

[greg g]

Personal preference of many forum members.

[jd52cranbrook]

Well, something has definitely changed to cause this to happen. I have never seen a electrode do that, now twice. Tomorrow I check the manifold, carb set up. Will try another set of plugs. I would really like to know what is causing it. I don't just want to "shot gun" things for a fix.

Tomorrow is another day.

Thank you for your help

[BeBop138]

JD, got a tough one there:(---far out thought---on the inside of the cap the brass for each plug tower shows the arc pattern from the rotor, check to see if the burn marks are the same on all towers---maybe the shaft is worn and not arcing the same on all cylinders---do the other dizzy you had mentioned---good luck........Lee

[jd52cranbrook]

Well,,,,

I put some colder plugs, 303s in it. And like I said before set the timing back to 4 btdc. Also closed the plug gap to 38.

50 miles, no issue, but I know its the long haul that's the test. Keeping my fingers crossed.