Reading spark plugs.

I decided to try some new spark plugs in my 300hp crate 360 magnum.
I was running the NgK v-power zfr5f11’s, I swapped them out for the Ngk v-power bkr5e plugs because the bkr5e has a shorter insulator on it andnive read the magnums run a little better with the shorter insulated plugs.
Anyways I pull all the plugs and they all look pretty good but cylinder 8’s plug is a little darker then the other 7.
I took a picture of the difference in it compared to the other 7.
What could be causing this?
The plug on the left is what the other 7 plugs look like.
The plug on the right is what came from cylinder 8 and looks to be firing different from the others.
I haven’t done a compression test in awhile but last time I did one all 8 cylinders were dead on at 150 psi and that was done with the engine fully warmed up at 190 degrees and at an elevation of 4200 feet above sea level.
It’s too late to perform a compression test on it tonight but I am going to check cylinder 8s compression tomorrow after work with the engine warm.
Just thought I’d share this to get some input and opinions.

For some reason the web page won’t upload my photo.
It says mb size is 2 and my phone says the mb size is 1.7.
So idk what’s going on there.

It WAS there.

It was sideways, but it was there.

and 1.7m is still too big. Should be a max of 30k if I remember correctly.

Well this site says 2mb and the original photo says 1.7mb
Anyways I posted it back up.
The number 8 plug smelled like fuel too when the other 7 plugs didn’t.
Any idea’s? I mean obviously a compression test on the number 8 cylinder is what I need to do next, which I will do tomorrow after work and I’ll report back.
Just has me worried cause I know the ignition is good.
And I’ve had this strange rough spot around 2500 rpm that I have not been able to eliminate no matter what I’ve tried.
I’m thinking it’s connected some how.

30k must be the sig picture, as I think about it.

If #8 is dark with carbon, and smells gassy, maybe the jet in the carb is loose and letting in too much fuel.

How are #6 and #8 ignition wires routed?

Missfires of #8 cylinder are a known problem if you do not have the correct (but weird) TSB wire routing correction.

http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v8.htm

They cross each other up above the valve cover.
I don’t have the wires routed based on that tsb.
But this is a carbed 5.9 magnum with a firecore 50 electronic vacuum advance distributor and a crane cams hi-6 cd ignition and a crane cams ps92 ignition coil.
And Taylor thundervolt 8.2mm plug wires.
Carb is a quickfuel super street series 680cfm vacuum secondary carb.
The last time I did a compression test all cylinders were at 150 psi and I’m pretty easy on this engine, I run premium fuel and synthetic oil and good filters and I don’t ever over rev it.
So it is kinda strange that cylinder 8 would all of a sudden develop an issue, because I know it hasn’t been miss treated since the last time I did a compression test.

An older Sun machine that shows all eight ignition traces at once on one screen would be valuable to insure there is no crossfire happening.

These single wire readout devices that give: peak KV, burn time in milliseconds, and burn KV

https://www.ebay.com/itm/Kal-Equip-Spark-Analyzer-2969-/202107367670?hash=item2f0e89b0f6

Have helped me.

I now have two I bought used so I can compare two cylinders at the same time,
or compare one cylinder to the averages of all eight by clipping to the coil output wire.

I like to see cleaner(lighter colored) plugs than that, yours look like there to rich on the mixture, especially at light part throttle cruise Those are both hot plugs
Synthetic oil will leak around intake gaskets and rings and can cause what your seeing, oil doesn't burn as easy as straight gas does
Do the compression check next
Usually when you have oil on the plugs they shine, yours doesn't look like they are, do they?

I agree with Cab. What you're seeing is fuel fouling. Your mixture is too rich on either plug.

R.

Here's the ;NGK color chart:

So why is only 1 plug doing this? Why do the other 7 plugs look different?
The other 7 have a tanish tint to them and don’t smell like fuel.
Number 8 was a little darker and smelled like fuel a little bit.
It’s been pouring rain all day so I wasn’t able to do a compression check on cylinder 8 after work tonight and I don’t have a shop anymore since I moved 😩
But I’m hoping tomorrow I can check compression in cylinder.
I’m going to purchase a wideband O2 to dial this quickfuel inn better with, I should have one and have it installed within the next month or so.
I have the carb leaned out quite a bit from the factory settings my higher elevation.
I’m at 3200-3500 feet above sea level.
Right now main jets are 64s and secondary jets are 74s, in running a 9.5hg power valve with .049 pvcr’s.
I have .033 high speed air bleeds, .063 idle air bleeds and .028 idle feed restrictors.
I have the 4 idle mixture screws set to the best vacuum reading, I get a solid 20hg of vacuum at idle.
Floats are set to half way up the sight glasses.
I’m running a .028 accelerator pump nozzle with a white pump cam.
Timing is 18 degrees initial, 32 degrees total all in at 3200-3400 rpm.
Vacuum advance adds an additional 12 degeees on manifold vacuum.
So I have 30 degrees at idle with the vacuum advance.
I don’t understand what’s got it running rich enough to affect only the number 8 cylinder.
I did raise the floats a little bit the other day and it felt like it made it run a little better because I did have them set at the bottom of the sight glasses.
But quick fuel reccoemnds half way up the sight glasses.
Maybe I’ll lower the float level a little bit and increase if the idle air bleeds since I appear to be fat on the idle circuit.
Then re-adjust mixture screws again.
I have some .070 idle air bleeds I can try and I have some .075 idle air bleeds as well.

Well, going to a wide band 02 censor will answer most your rich / lean concerns. I think you are going to find you are pretty close to where you want to be. 7 plugs look good. Also doubt your comp. test will show anything. My guess is that you have a valve guide seal leaking a bit in #8. If you could get to a intake / exhaust port visual in that hole you could probably confirm it.

I think you need to move the vacuum hose to the distributor to above the throttle plates instead of running it underneath them on manifold vacuum, try that and let us know how that works on your car
I would try moving the total timing up to 33 to 35 degrees also for your altitude The higher you go in altitude the thinner the air, which takes a little longer to reach peak burn rates and temperatures also

I have not kept an exact count but my fuzzy memory is that i have read more posts about the Magnum V8 having a blown head gasket on #8 cylinder than any other cylinder.

I also seem to remember that when the Evans Cooling company ran a test of their waterless coolant in Magnum 5.2V8 Jeeps of the Detroit Police Dept they suffered blown #8 head gaskets and had to enlarge the block/gasket/cylinder head passages at the rear of the V8.

Wouldn’t I be seeing eveidence of a blown head gasket in the oil and the coolant?
I also forgot to mention that this is a very low mileage engine.
It only has like 30k miles on it.

Unless you have a miss, the reason that one plug shows richer is due to the fuel distribution of the manifold you are using. I would reroute the plug wires in accordance with the TSB and see if that doesn't fix it for you. A symptom from the TSB "various single cylinder misfire (1, 3, 7,) and especially 5 and/or 8"

It is not a blown head gasket.

I will try and figure out a way to separate wires 6 and 8 so they don’t cross each other above the valve cover.
I find it hard to believe it’s a blown head gasket or a leaky valve seal as well.
This engine is very low mileage, like I said it’s around 30k and half it’s life was fuel injected. It’s only had a carb on it for about 15k of it’s miles.
Since I raised the floats I’m also going to lean out the idle air bleeds and see if that helps.

This comment caught my eye.... Were they too low?? There is only a wrong float level or correct float level....

If your float level is too high I could see this causing at least part of your problem......

Guys - how do you get a very dirty plug with a blown head gasket? There are several other choices that are easier to work with and more likely to be the root cause. They have been described above.

A 300hp crate motor has a carbureted intake. Any time air/fuel mixture flows through a manifold there will be unequal fuel distribution. So your #8 could have a river of fuel running down the bottom of the plenum into the runner. I have an old Direct Connection engine manual that details how to epoxy popsicle sticks into the plenum to help even out the mixture.

R.

I am trying to offer ideas to the OP.
Without being there to check other signs it is admittedly hard.

If compression is low in #8 there will be a missfire and unburnt fuel,
or if there is induction tiggered missfire in #8 from #6 ignition wire,
in either instance i would expect to see a gasoline wetted sparkplug.

I would expect if the manifold distribution is really bad to # 8
then the symmetrical other runner of the M1 dual plane would show at least some sign of bad distribution, but a really badly malfunctioning carb can do unpredictable things.

A video boroscope with a 9 mm camera head to go through the sparkplug hole and also down intake runners could narrow this long distance troubleshooting down. These are value priced now days.

Runners

That is the intake manifold I’m running.
Part of the confusion on the float level is holley reccoemnds the fuel to be at the bottom of the sight glasses, quick fuel reccoemnds having the fuel half way up the sight glasses.
So I did have the float level at the bottom of the sight glasses, I noticed when it was cold out especially that it was pretty lean at part throttle.
Specially after I slowed my advance rate down in my distributor.
So I raised the floats to half way up the sight glasses and that solved the lean spot at part throttle and made the engine feel like it was running better, specially when it’s cold.
So I’m tninking since I raised the float level to what quick fuel reccoemnds that I probly
Should increase the idle air bleeds to lean out the idle and off idle circuit a little bit.

Or maybe lower the floats back down a little bit so they are 1/4 of the way up the sight glasses instead of half way up.
I just figured I’d set the float level to what is specified by quick fuel since it is a quick fuel carb.