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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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Discussion Starter · #3 ·
I’m still running breakin oil. I will drive it around. These are autolite 3924. I was thinking of switching to NGK. Where could the oil be coming from? The engine was just built by a reputable builder.
 

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Discussion Starter · #8 ·
I worded it wrong. I meant the stinky rich eye burning smell. I fixed that. Looks like I need to change plugs to hotter plugs and drive it hard. Then check again.
 

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Discussion Starter · #23 ·
I just hope it’s not this AED 750 carb. I found a few complaints online about them idling pig rich. Not many but they are there. Something about too many emulsion holes.
 

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Discussion Starter · #25 ·
Good point. Still learning here. IFR are .033 and IAB are .075. I’ll try to find that forum where they said that.

I have the primarily curb idle stop screw set to exactly 3/4 turn. This leaves the primary T-slot to .020. Primary blades have 1/8 holes drilled in them. Secondaries have the higher T-slots on this unit. To maintain 900 RPM, I have to open them to 3/4 turn. All 4 idle mixture screws happy and sensitive at 1-1/4 turn. Ignition locked out at 36. Idle is clean here. The problem is a lean backfire through the carb on hard acceleration. So, when I close the secondaries to 1/2 and open the primaries to 1 full turn exposing .030 T-slot, the lean carb backfire goes away, it hauls ass, except the idle stinks, burns my eyes, and blackens plugs. Not to mention the primary idle mixture screws go numb. They work a little, but closing them won’t stall the engine.

Should I get a hotter plug than the FR5?
 

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Discussion Starter · #29 ·
I found this on yellow bullet…..


“keep it up to at least 2200 when you first start it up, and run the HOTTEST spark plugs you can find. If the carb is right , these little things should really help out.Never let it idle slow when it is cold. Plug fouling is almost always from improper startup proceedures.
JOE SHERMAN RACING”

Any truth to this? I have an HP body so no choke. I hold the idle to around 1500 to warm up.
 

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Discussion Starter · #31 · (Edited)
Great info. I’m open to all advice because I’m still learning. This unit came from AED with drilled primaries. The hole size is not specified. Neither is the IFR size. All other specs are detailed in the carb card.

The backfire through the carb on hard acceleration only happens with the secondaries open to 3/4 turn. This clean up my idle due to being able to close the primaries to where the primary T slot is only .020. Clean idle but stumble and back fire.

When I close the secondaries to 1/2 or less, acceleration is awesome! But now I have to open the primaries to where the t-slot is at .030. Then the idle gets fat again. Stinks and blackens plugs.

This is all to maintain a 900 rpm idle in park / neutral. Around 800 in gear. Could I be chasing too high of an idle? Lowering the idle to 800 in neutral would theoretically give me the best of both worlds. However, will that be an issue with the cam?
 

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Discussion Starter · #33 ·
i have not touched anything other than primary and secondary idle snd 4 mixture screws. The squirters are both #31. I don’t want to screw things up worse.

the front blades are drilled 1/8. It came that way. Should I drill the secondaries 1/8 or like 3/32 to start?

I stuck with the idle circuit as the culprit due to the black plugs and how I can get rid of the lean carb backfire by giving it more transition.

I think you are on to something…. Leave the primaries to .020 transition where the 4 idle mixture screws like are become sensitive. Then drill the secondaries to close them to get rid of the lean backfire. Then add more squirter if needed.
 

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Discussion Starter · #37 ·
Starting with the squirter does make sense. They are easy to get.

the cam is a Comp Cams XR282HR 230/236 @50 110 lsa retro roller. 3200 stall 9.5 inch converter.

The engine would not even start under 20 degrees initial. 20-30 and it ran like ass. I called my engine builder and he says that recipe he built calls for locked out timing. It didn’t even start to idle ok until 30 degrees. I figured what’s the point of adding 6 degrees of advance. 36 runs good.
 

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Discussion Starter · #39 ·
Yeah that’s me. It’s a full electronic distributor. It has start retard and full lock out feature option. It cleaned up the smell but not the black plugs.

I checked my balancer and TDC like ten times. It’s dead on.
 
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