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Spark plugs black

3171 Views 114 Replies 9 Participants Last post by  ericnova72
Hello all,
Can you take a look at these plugs and tell me what’s going on? I just installed them and have only idled this freshly rebuilt and already broken in cammed 383 stroker. The strap is shinny black. The center electrode is flat black. These are brand new Autolutes 3924. I was fighting a very rich stinky idle with this AED Holley 750 DP, but fixed it and trashed the old fouled plugs. I’m running MSD 6A and a lot of timing at idle. 36 degrees.
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Too much fuel. This might have been too long of an effort to get it up and running, choke closed too much, carb or injection running rich, spark plug heat range too cold common especially with aluminum heads. Etc.

Need more details about cam heads, compression ratio, what’s mixing fuel and air, operating temperatures, what ignition system and spark plugs not to mention how initial start up and subsequence running have been.

These modern peanut plugs are pretty much shot once they look like this, start over with a fresh set and unless you’re using a Capacitive Discharge (CD) ignition like a 6AL or better get the plug gap to .030 to .040 inch.

Bogie
 

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I looked up the FR5 and they are exactly what AFR calls for.
A good place to start. keep in mind that a lot of these heat range recommendations are for racing where there is a lot of heat. So don’t be surprised if the recommended plug is a bit cold on the street. This is just a cut and try exercise to dial it in. I have a large grungy spark plug collection, I keep ‘em for protecting the spark plug threads when painting heads.

Bogie
 

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Really need to know cam being used that will establish the idle speed by virtue of what RPM is needed to keep the engine taching over.

Stall speed on tge converter is good info as will but only a 100 rpm loss from free idle to in gear sounds like some sort of higher stall converter.

Since you have a 6AL box I don’t expect you have misfires, capacitive discharge usually fires the plug through a lot of gunk on the insulator.

You are running one hell of a lot of advance, having it all in at idle indicates a big time racing cam. Is this what’s in there? Lots of base advance makes an engine hard to start. I separate the ignition on these full race engines from cranking so turning the engine over doesn’t turn on the ignition at the same time. So I put the ignition on a separate switch so tge starter can get some spin on the crank before dumping extremely advanced ignition on it. Another trick is vacuum advance with a more conservative base so the high amount of idle advance doesn’t kick in till the engine is running. This takes having an adjustable vacuum can on the advance when a big cam that doesn’t generate a lot of idle vacuum. A problem you might get into with such a combination is the vacuum usually spikes rather high for a moment as the throttle just tips in raising the RPMs at a fast rate which pops the vacuum advance up suddenly and temporarily.

I like to set the primary side idle throttle blades just into the range that exposes .020 to .030 inch of the transition on the primary side. The rear only opened enough to get enough air to achieve the idle speed the engine is looking for with none to very little fuel. I make no attempt to equalize the primary and secondary settings. I saw an Uncle Tony’s Garage vid the other day where he has picked up on a trick a used for a long time of using aquarium air bleed adjusters to feed extra idle air while trimming the fuel only on the primary side.

Big cams at idle or low speed cruise are given to high amounts of reversion. The problem with this is a carb will add fuel to flows going out the air horn as well as flows coming in so it’s easy to get way fat mixtures at idle through midrange RPM’s till the port velocity gains enough inertia to quell the reversion.

Idle and putting around with a big cam is just a PIA and that’s just the way it is. Port or direct injection is a big help for this condition but big cams go beyond what self learning systems can do, so like everything else there are limits to simplicity where that ends custom tuning comes in and that quickly gets expensive.

Bogie
 

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Right now I wouldn't sweat the black plugs, it is not likely they will ever be anything but black ever again. What I’d want to see is for them to dry out and the over rich smell to lessen but with that much cam will probably will not go away entirely.

As long as you don’t get misfires and with a 6AL you probably won’t I wouldn’t worry the insulator color they’re dirty carbon color and will probably stay that way. Obviously you won’t be able to read those plugs in the future but until your sure it isn’t running dirty rich which you can smell I just wouldn’t worry about reading plugs just yet.

I forgot that you had a distributor that electronically resets the timing when cranking so if it takes 20 degrees out I could see it having a hard time getting going if you back out 20 or so degrees from the static setting.

I set things up for myself mostly the old fashion way as after 54 years in aerospace I‘ve seen enough of the combination of electronic failures and asleep at the stick air crews to know that when something electronic goes out or temporarily fixes a problem the crew doesn’t know about such that the operator is situationally unaware things go to poopoo mighty quick when the automatic system either dies, glitches, or runs out of its limits of authority.

Bogie
 

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Or warped metering blocks leak same for main body. Sounds like a carb disassembly is in order so these flange surfaces can be inspected for straight and flat and the gaskets them selves can be looked at however unless these are the coated type gasket the standard Holley gasket usually doesn’t survive disassembly.

If the engine is not sensitive to idle mixture screw adjustment it’s getting fuel from somewhere else. That can be the transition circuit, dripping off the main venturies at idle or leaking past internal gaskets or poor fitting major parts. The latter is not uncommon.

Bogie
 
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