Help reading spark plugs
Thread Starter
Melting Slicks
Joined: Apr 1999
Posts: 3,264
Likes: 3
From: Toms River NJ
Help reading spark plugs
I threw this in another thread as well, but isnt exactly the right Title for my questions on reading spark plugs...
Ok I pulled a few plugs and they all more or less look like the pics below. I think there might be some detonation on the porcelain?? As far as the heat strap, there seems to be the reat heat range, and as far as jetting on the base ring, I really couldnt make it out... All these reading were from the plug pulled from the last time I drove the car... and Ive read that they need to be read after a WOT run and shut down immediately... After I wentout and did a WOT run in 3rd gear to about 100mph I shut it down, but my damn motor likes to pre-detonate or whatever you call it, when you shut it off and it keeps surging around. In any case, the plugs looked just like they did before I made the run and same as the pics below...
Can anyone tell me if it looks like im running lean, rich, detonating?
Or can I not get an accurate reading cause the motor is surging/detonating when turned off?
Thanks again... Chris
Ok I pulled a few plugs and they all more or less look like the pics below. I think there might be some detonation on the porcelain?? As far as the heat strap, there seems to be the reat heat range, and as far as jetting on the base ring, I really couldnt make it out... All these reading were from the plug pulled from the last time I drove the car... and Ive read that they need to be read after a WOT run and shut down immediately... After I wentout and did a WOT run in 3rd gear to about 100mph I shut it down, but my damn motor likes to pre-detonate or whatever you call it, when you shut it off and it keeps surging around. In any case, the plugs looked just like they did before I made the run and same as the pics below...
Can anyone tell me if it looks like im running lean, rich, detonating?
Or can I not get an accurate reading cause the motor is surging/detonating when turned off?
Thanks again... Chris
Thread Starter
Melting Slicks
Joined: Apr 1999
Posts: 3,264
Likes: 3
From: Toms River NJ
Instructor
Joined: Nov 2004
Posts: 194
Likes: 0
From: Appleton Wi.
Do you see that bit of heat discoloration near the end of the ground strap, that tells you where your timing is. Near the end of the strap, where it is, would be a little too far advanced. Back off your timing a couple of degrees and give 'er another go. See if it moves to the bend in the strap where it should be. It looks like you could richen it a tad, but if you do you will move the timing mark also, because you are cooling the motor by adding fuel, that mark is directly affected by heat, and amount of fuel.
This is purely my own philophy.
TJ
This is purely my own philophy.
TJ
Drifting
Joined: Mar 2006
Posts: 1,526
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From: Oak Ridge NC
Thread Starter
Melting Slicks
Joined: Apr 1999
Posts: 3,264
Likes: 3
From: Toms River NJ
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Thread Starter
Melting Slicks
Joined: Apr 1999
Posts: 3,264
Likes: 3
From: Toms River NJ
Thats what I've been thinking, but how did you guys come to the conclusion? Because the porcelain is soo white??
And if its lean, how many jet sizes would you suggest going up at a time... I dropped 3 sizes down before from the way it came from the factory (Speed Demon) since everyone said it was too big a carb for a zz4. Would 3 jet sizes make it that bad?
Safety Car
Joined: Aug 2001
Posts: 3,892
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From: Pettis Performance 565 with two stages of Nitrous Supply nitrous 1.082, 4.61 at 155, 7.17 at 192
Were these plugs new, run at a WOT blast, shut off and then pulled?
If it is surging it is likely detonating a little. I see the little pepper marks on the porcelain, can you look at them under a magnifying glass and see any shiny flakes? (aluminum) the little black specs could also be oil, not likely if they all look like the plug you posted.....do all the plugs have the little black specs ?
What gas are you using ?
Have you ever seen how racers cut the threads off a plug to expose the fuel ring at the bottom of the porcelain? can you do this after you make a clean pass with a fresh plug?
If it is surging it is likely detonating a little. I see the little pepper marks on the porcelain, can you look at them under a magnifying glass and see any shiny flakes? (aluminum) the little black specs could also be oil, not likely if they all look like the plug you posted.....do all the plugs have the little black specs ?
What gas are you using ?
Have you ever seen how racers cut the threads off a plug to expose the fuel ring at the bottom of the porcelain? can you do this after you make a clean pass with a fresh plug?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Sorry. I don't see much of anything wrong with those plugs. They aren't carbon-ed up, the electrode isn't eaten up, no oil fouling, light tan color on end of porcelin... are you having a problem with them?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Follow-up: If you are having "engine run-on" problems, it isn't the plugs. The pre-injection 70's engines had various means of shutting the engine down without run-on (dieseling) issues. My '71 w/A/C turns on the A/C clutch when the engine is shut off so that there is a "load" placed on it. Your '74 probably has a different method (but I don't know what it is). I would guess that whatever "shut-down" system yours came with is not working properly.
Safety Car
Joined: Aug 2001
Posts: 3,892
Likes: 13
From: Pettis Performance 565 with two stages of Nitrous Supply nitrous 1.082, 4.61 at 155, 7.17 at 192
The run on is probably caused by crappy gas, a little compression, and too much timing. If he stuck a tank full of race gas in the car there is about a 99% chance it would not run on
Melting Slicks
Joined: Jan 2004
Posts: 2,527
Likes: 1
From: St. Petersburg, Fl///Columbus, Ohio
When you asked about Carb Jet sizes in your other thread I replyed..
I'd back the Timing up 2Deg & richen up the Idle Circuit a little and check the fuel filter before you drive it
Call them and ask!!!
When I called Holley and eldelbrock I told them what I had & they told me what Jets..... The Eldelbrock is dead on, I haven't tried the Holley yet but they sounded like they knew exactly what jet kit to use.
Contact Technical Support (706)864-8544 before making any calibration changes
Last edited by jcswm; Jul 10, 2007 at 03:43 PM.
Thread Starter
Melting Slicks
Joined: Apr 1999
Posts: 3,264
Likes: 3
From: Toms River NJ
Thread Starter
Melting Slicks
Joined: Apr 1999
Posts: 3,264
Likes: 3
From: Toms River NJ
Thread Starter
Melting Slicks
Joined: Apr 1999
Posts: 3,264
Likes: 3
From: Toms River NJ
Follow-up: If you are having "engine run-on" problems, it isn't the plugs. The pre-injection 70's engines had various means of shutting the engine down without run-on (dieseling) issues. My '71 w/A/C turns on the A/C clutch when the engine is shut off so that there is a "load" placed on it. Your '74 probably has a different method (but I don't know what it is). I would guess that whatever "shut-down" system yours came with is not working properly.
Melting Slicks
Joined: Jan 2004
Posts: 2,527
Likes: 1
From: St. Petersburg, Fl///Columbus, Ohio
