Read my plugs, was carbon fouling on 93 pump gas but not on 96 vp?

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71DodgeDemon340

71DodgeDemon340

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Hey guys i just was wanting to get some guidance on this subject, ever since i had the 340 in my demon rebuilt when i restored it the plugs always look carbon fouled, ive never had a miss caused by it but they always look black. I change them every 2 years and never have a issue, im just wanting to know possible solutions or things to rule out. Now a little bit on the engine build, 69 340 block, bored .040 over, lunati voo doo cam (dont remember the specs but its not a extremely aggressive cam) edelbrock performer rpm heads, edelbrock performer rpm dual plane intake, edelbrock thunder series avs carb 650 or 700 cfm cant remember with about a 1/2” spacer/heat shield. Compression is estimated at around 10:1 maybe a little less. Running mopar chrome box ignition with a distributor from trail beast. Taylor ignition coil. Taylor thundervolt plug wires and ngk plugs. Initial timing set a 16 degrees btc and all in is around 34-36 at 2000 rpm. Engine was dynoed by the engine builder so im assuming they tuned it as well but im not sure if the jet size has been changed or not from what the carb ships with. Its been about 10 years since the engine has been built and only thing ive done to the carb is adjust the idle speed, the electric choke, and the idle mixture once. Only have ran 93 non ethanol pump gas but have recently switched to 96 vp non oxygenated fuel since there have been issues with bad gas in my town. Edelbrock recommends a RC12YC plug for these heads in which ive been running the equivalent NGK BKR5E V Power plugs. I plan to pull all 8 plugs tonight and post pics to have you guys advise me the best course of action. One question i have is carbon fouling almost always related to spark plug heat range? Or is it more common to be too rich?
 
Heres plugs from Cylinder 1 3 5 7

Cylinder 1

55419BB5-DED8-4060-8801-1D9A4108B9EC.jpeg


5FB5C687-A348-4207-BB55-244FD28CEF8C.jpeg


Cylinder 3

4999F93D-DF7A-46A8-9F4A-F39E8BC45515.jpeg


84D7955A-6251-486D-89BC-63027C805BBF.jpeg


Cylinder 5

26B70865-9B1E-4C72-8C08-FBBD27E3DD7C.jpeg


5F7E88FD-5183-456E-9ADD-E3E331362D2A.jpeg


Cylinder 7

F7689EFF-42C2-418B-A5C6-1E3CBB27041A.jpeg


DC7946DE-0C25-4BEF-9E63-116290C49D12.jpeg
 
These plugs are a little over 2 years old, no change to carb or anything else since, have been using vp 96 octane non oxygenated fuel for about 6 months. The plugs have never looked that good, they have been pretty much all black on 93 non ethanol
 
To me it looks like rich with too much timing and maybe even a step or two of too hot a plug.
 
Maybe a good time to try so?e non projected ngk R5671a-7 or ngk R5671a-8 which is colder than the one ending in 7.
 
QuickDart360 said:
Maybe a good time to try so?e non projected ngk R5671a-7 or ngk R5671a-8 which is colder than the one ending in 7.
Click to expand...

Whats the benefit of a non projected plug? Also what is the determining factor or what you look for to determine heat range?
 
My motor is pretty close to your build outside of it being a 5.9 running a 770 Street Avenger.
This is a 4 year old NGK GR4 V power which I pulled recently that I consider just about perfect.
The ring being dark on them is normal, but yours being that dark and the center being that light is a clue of a hot plug.
Also notice where the strap color change is on them.
Yours is way down by the ring, vs mine being about the middle of the bend.
(Timing too high)

That’s my opinion anyway. :D

D8800C0B-D6ED-411F-8B33-5DC51096C312.jpeg


23A815D6-D36D-4B91-9843-075529027EDF.jpeg
 
TrailBeast said:
My motor is pretty close to your build outside of it being a 5.9 running a 770 Street Avenger.
This is a 4 year old NGK GR4 V power which I pulled recently that I consider just about perfect.
The ring being dark on them is normal, but yours being that dark and the center being that light is a clue of a hot plug.
Also notice where the strap color change is on them.
Yours is way down by the ring, vs mine being about the middle of the bend.
(Timing too high)

That’s my opinion anyway. :D

View attachment 1716071299

View attachment 1716071300
Click to expand...

Are you referring to initial or total timing by that mark? Is the initial timing closer to the end of the ground strap or the base? Ive seen some charts and they show being able to see 2 timing marks on the ground strap?
 
I'll guess fat at idle.

What vacuum is it pulling and are the factory step up springs in the carb. Might need lighter springs.
 
71DodgeDemon340 said:
Are you referring to initial or total timing by that mark? Is the initial timing closer to the end of the ground strap or the base? Ive seen some charts and they show being able to see 2 timing marks on the ground strap?
Click to expand...

Change of color up towards the tip is late timing, and more towards the threads is too much.
Middle of the bend is about perfect IMO.
If you idle or low rpm a lot then yes, idle is a bit rich.
(And I still think it may also be too hot a plug)
 
Those plugs being two years old makes it almost impossible to get a WOT read on. That being said, my opinion is you are 2-3 degrees short on timing for max power. And probably a full afr point rich at idle. The heat range looks close, maybe one step too cold. If that were my engine I’d dial in the idle afr as lean as it will idle happily, and see if it helps the sooty look of the top of the threads. If not, it would get one heat range hotter plug. Then I’d add 2 degrees of total timing, put a new set of plugs in and start looking at wot fuel.
 
We had a discussion on the proper plug for the 340's not too long ago. I was using recommended by the parts supplier catalog, N12Y champions. N9Y were originally called for by Chrysler. Mine ran better with the cooler N9Y. My compression 10.5.
 
TrailBeast said:
My motor is pretty close to your build outside of it being a 5.9 running a 770 Street Avenger.
This is a 4 year old NGK GR4 V power which I pulled recently that I consider just about perfect.
The ring being dark on them is normal, but yours being that dark and the center being that light is a clue of a hot plug.
Also notice where the strap color change is on them.
Yours is way down by the ring, vs mine being about the middle of the bend.
(Timing too high)

That’s my opinion anyway. :D

View attachment 1716071299

View attachment 1716071300
Click to expand...
Dang boy. Cut them fingernails. Gross.
 
Woodys_Cuda said:
We had a discussion on the proper plug for the 340's not too long ago. I was using recommended by the parts supplier catalog, N12Y champions. N9Y were originally called for by Chrysler. Mine ran better with the cooler N9Y. My compression 10.5.
Click to expand...
There are so many variables to consider when choosing a “correct” plug. Change any one of those variables from stock (intake manifold, camshaft, compression ratio, piston design, chamber design) and the book may as well go out the window. Test test test.
 
TT5.9mag said:
Those plugs being two years old makes it almost impossible to get a WOT read on. That being said, my opinion is you are 2-3 degrees short on timing for max power. And probably a full afr point rich at idle. The heat range looks close, maybe one step too cold. If that were my engine I’d dial in the idle afr as lean as it will idle happily, and see if it helps the sooty look of the top of the threads. If not, it would get one heat range hotter plug. Then I’d add 2 degrees of total timing, put a new set of plugs in and start looking at wot fuel.
Click to expand...

Ok trail beast says too much timing and too hot of a plug, you say not enough timing and too cold of a plug. Lol
 
So why the drastic change going from 93 non ethanol pump gas to 96 vp non oxygenated race fuel? Before on 93 the porcelain was black
 
Oxygenated fuel vs non oxygenated fuel along with race gas vs pump gas will all require different tune ups. You cannot compare them to each other. For example, on the dyno running my twin turbo big block, pump 91 California junk gas vs sonoco 110 was a 2 jet number change in the front and 4 jets in the rear to maintain a similar afr. When you changed fuel you changed your required tune up. And you must have changed it for the better.
 
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