READING 70 SWINGER 340 SPARK PLUGS

For all the tuner guys. I have a friend over with his car and we are playing with his ARF gauge tuning has motor. Idle 14.1, cruise 13.5 and Wot 12.5. Take a look at his number one spark plug after a run, what's your opinion on how it looks?

What brand plug is it?

If it's a Champion, it's about two ranges too hot, rich at a cruise and most likely at WOT. It needs more timing, or a quicker timing curve.

If it's an NGK, it's about 1 range too hot and the rest is the same.

If it's an Autolite, I'd be guessing.

I'd still like some better pictures.

What is 'a run'? If you wind it out in all 3 gears, then let off and cruise home, and only then pull the plugs, you won't see what the fuel conditions are at WOT; the engine operation at cruise going home will mask it. If you want to take plug read for WOT, put in a clean set, drive to where you can got WOT as far as you can, then at the end of the WOT run, cut the ignition, drift to a stop and pull plugs and read. (Of course, you gotta be careful with losing any power steering and maybe power brakes, and the old steering columns that locked when you cut the ignition!)

What fuel is being used? The modern pump fuel seem (to me) to look lean on the plugs.

The look of carbon on the outer edges looks rich. And I would guess that it is rich at cruise and probably so at idle. Can't say myself for WOT. 13.5 AFR is richer than I run on flat level ground, steady throttle, 55-65 mph; I look for around 15 under those conditions.

And beware that AFR's will read lean at idle until the engine is fully warmed up. So don't take AFR readings while the engine is cold or ever warming up.

Can you tell us a bit more about the engine?

Champion plugs RN12YC Copper with .35 gap, 18 degrees of timing at idle, all in by 2800

d1970 said:

Take a look at his number one spark plug after a run

Click to expand...

What do you mean after a run? The plugs will show you the status of the engine at shut down. So to read idle tune, shut off at idle and pull plugs, or shut off at WOT, pull plugs, shut off at cruise, pull plugs.. Can we see a very close pic of the ceramic?

JoeSBP said:

Spark plug reading can be complex and sometimes frustrating task this page will help make it easier and the results rewarding

Click to expand...

yes I have that article already, car was run through the gears WOT, then stut off the motor and coasted to a stop and we removed the #I plug and replaced it with another one for the drive home

Can you tell us a bit more about the engine?

stock 340 32,500 miles on it, 4 gear with 3.91 rear gears

d1970 said:

Champion plugs RN12YC Copper with .35 gap, 18 degrees of timing at idle, all in by 2800

Click to expand...

If that's the case. I'd leave the 12's in there and put some more initial in it and try and get 35*'s total by 2500 RPM.

Then start working on the idle and cruise circuits of the carb. It's rich. You should see white on the porcelain all the way down to where the shell meets the porcelain. Do WOT runs as the last thing you do.

Unless you are trying to run Bob Utner down for the money, I almost never do a clean kill and pull plugs at the end of the track. I drive back and look at them.monce you get the hang of reading plugs you'll know what to look for.


BTW, you want the ground strap clean to half way down to the shell not in the bend if you are on pump gas.