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Spark plugs, misfires, and general ignition system

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mtrosclair View Drop Down
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    Posted: Mar/24/2023 at 1:38pm
Good afternoon folks I’ve been getting a slight misfire at idle and at constant engine running speeds so today I decided to go ahead and pull the plugs and look under the rotor and see what was going on. The spark plugs all look about the same I’m posting a picture (#1 is on the right, #6 left) so any spark plug gurus can tell me if they look right or not, from what I can find online this seems to be a proper color. These plugs having about 400 miles on them total. When I pulled the cap, there is some arcing evidence near the five and three cylinder terminals, I’m wondering if whatever is causing this could be the reason for my misfire. I have ordered plug wires, and new plugs, just to remove those as a possibility of being an issue.

While looking for spark plugs, however I did observe that they make an HEI distributor that fits the engine, I am wondering if that would give me smoother ignition then I’m currently experiencing with the stock distributor, with an electronic module installed. 







Edited by mtrosclair - Mar/24/2023 at 1:40pm
1963 Rambler Classic 550
Originally a 196, this one has a 199 from a 69 American.
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Trader View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2023 at 2:15pm
Well you can print this out to read your plugs:
IMO the plugs are good.
But the distributor cap is saying there is a problem. The arc tracing on 3 of 6 plug terminals, 2 being not good at all indicate there is a problem. It could be the cap, but first guess since they are all one side is the distributor shaft or gear may be worn.
A coil/points/condenser will usually have indications on all plug terminals.
The other possibility is 3 bad wires and if those worst arc lines are cylinders 5 + 3 then I'd start there and replace the rotor/cap.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mtrosclair Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2023 at 2:42pm
Originally posted by Trader Trader wrote:

Well you can print this out to read your plugs:
IMO the plugs are good.
But the distributor cap is saying there is a problem. The arc tracing on 3 of 6 plug terminals, 2 being not good at all indicate there is a problem. It could be the cap, but first guess since they are all one side is the distributor shaft or gear may be worn.
A coil/points/condenser will usually have indications on all plug terminals.
The other possibility is 3 bad wires and if those worst arc lines are cylinders 5 + 3 then I'd start there and replace the rotor/cap.

I’ll pick up a new cap and rotor today and try that first.  

Thoughts on something like this?

1963 Rambler Classic 550
Originally a 196, this one has a 199 from a 69 American.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2023 at 2:53pm
With that distributor your going to have to wire it for full 12vdc, need newer ignition wires and modern spark plugs.
With that output voltage jump it would be well advised to ask others that have that distributor what spark plugs they are running as the heat range will likely need to change for optimum performance/longevity.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2023 at 3:14pm
Points, rotors, and caps are old technology. The ability to score good products has vastly reduced in the last couple of decades. Your problem may be as simple as a bad cap casting. Then again, it may not. Replacing the the cap and rotor may not help. Then again, it may. Do you see a theme developing? Smile

Electronic ignition should not improve the running characteristics of a street driven points/condenser ignition. However, if the product quality is better, then it just might. There are good good conversion distributors and bad ones. To be honest, I don't know the status of the one in your link.

If you do go electronic, don't forget about the resistance wire which drops voltage to the coil. Electronic systems may require full 12V.

You might investigate Trader's suggestion of worn distributor bushings before dropping coin on electronic ignition. If you do the fix yourself, it will be cheaper.

The first car I ever drove had a 199 in it. It may not have an overabundance of power, but it took abuse from three teenagers and lived to tell the tale. Good solid engine IMO.
69 Javelin SST BBO 390 T10
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mtrosclair Quote  Post ReplyReply Direct Link To This Post Posted: Mar/24/2023 at 5:01pm
Plugs, wires, and a rotor cost me a grand total of $41 at AutoZone. I swapped all of that out with the new spark plugs correctly gapped and that seems to have resolved the issue. I was going to do one part at a time to kind of figure out what was the actual cause, but we have some rain on the forecast and I didn’t want to run out of time.

The HEI distributor does intrigue me, although I don’t know if there would really be any advantage to a vehicle like mine, other than reducing the amount of installed parts.
1963 Rambler Classic 550
Originally a 196, this one has a 199 from a 69 American.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Mar/25/2023 at 2:38am
The carbon tracks on the two adjacent terminals but not on the other four terminals is concerning. Perhaps the cap was installed improperly at an angle. 

Pertronix modules are practically immune to worn distributor bushings, unlike points.

The ignition timing could be wrong as well. Over-advanced timing can cause an engine to stumble in a way that feels like a misfire. People often crank up the timing thinking more is better (not the case), so if you do not know what the timing is set at currently, I suggest checking it. 
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1972 Wagoneer
1973 Ambassador
1977 Hornet
1982 Concord D/L
1984 Eagle Limited
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mtrosclair Quote  Post ReplyReply Direct Link To This Post Posted: Mar/25/2023 at 8:40am
Originally posted by FSJunkie FSJunkie wrote:

The carbon tracks on the two adjacent terminals but not on the other four terminals is concerning. Perhaps the cap was installed improperly at an angle. 

Pertronix modules are practically immune to worn distributor bushings, unlike points.

The ignition timing could be wrong as well. Over-advanced timing can cause an engine to stumble in a way that feels like a misfire. People often crank up the timing thinking more is better (not the case), so if you do not know what the timing is set at currently, I suggest checking it. 

I am running a perteonix currently, the miss at speed is gone but the idle is still “lumpy”.  Timing is at around 9 btdc hot with vac advance disconnected. I was running 6 BTDC before but a friend of mine that’s an old school mechanic said that wasn’t enough and might be the cause of my miss. 


Edited by mtrosclair - Mar/25/2023 at 8:42am
1963 Rambler Classic 550
Originally a 196, this one has a 199 from a 69 American.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Mar/25/2023 at 8:03pm
You need to check your manual for the correct timing specification and setting procedure. 10* BTDC at 500 RPM with the vacuum hose disconnected sounds about right. If it runs better with the hose disconnected, that tells you something. 
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1966 Marlin
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1973 Ambassador
1977 Hornet
1982 Concord D/L
1984 Eagle Limited
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mtrosclair Quote  Post ReplyReply Direct Link To This Post Posted: Mar/25/2023 at 8:29pm
Originally posted by FSJunkie FSJunkie wrote:

You need to check your manual for the correct timing specification and setting procedure. 10* BTDC at 500 RPM with the vacuum hose disconnected sounds about right. If it runs better with the hose disconnected, that tells you something. 

I don’t have the manual for this engine as it’s not the original, it’s out of a 69. I will adjust to 10 degrees and see how it does. 


Edited by mtrosclair - Mar/25/2023 at 8:34pm
1963 Rambler Classic 550
Originally a 196, this one has a 199 from a 69 American.
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