Reading Spark Plugs to Adjust Mixture

[ibmiked]

I've recently switched from an old set of Bosch WR6DP to NGK B6HS in my slightly warmed over 2.0L. I thought I might give the hotter NGK a test and see if there was any more power. I have an MSD 6 ignition and coil. I just put 200 miles of slightly agressive driving on the car, with the last 50 being highway miles are varying (but high) RPM. I noticed a slight pop on lift off, so decided to pull the plugs for a report card and to do some fine tuning. I've always used my plugs as a kind of tea leaf to check up on the motor, but I realize that there are many here who can read them better than I can.

I'd love some input before I start tweaking the idle mixture on my Weber 40's. I'm just looking to see if my instincts are right here, and maybe I can get the car into better tune with a few more heads to scratch than just mine.









My instinct is to enrich #2 and maybe lean back #5 a bit. I'm also a little concerned as I'm seeing a pinkish-brown on the porcelain of #4 & #6, which I think means these plugs might be a touch too hot. The car ran at 185-190 degrees today with an ambient temp in the mid-70's F. This is up from the normal rock-solid 175 degrees F that the Bosch ran.

Anybody else want to take a stab?

Thanks, Mike

[hoffman912]

You cannot read sparkplugs today with modern unleaded gas.

[Steve@Rennsport]

Hi Mike,

Reading plugs in engines that use unleaded fuels isn't impossible, just different. Its still an bit of an art form that does take years of experience to get it right.

One needs to carefully inspect the porcelain in close detail for meaningful information with a strong, illuminating magnifying glass so your pics don't work. Further, one needs to perform a "plug cut" where the engine is suddenly switched off while running at a particular RPM and throttle position to get anything useful. This gives a nice "snapshot" about fuel mixture for someone who knows what to look for on the center conductor. There is a subtle ring that shows up on there to tell you about combustion temperature, along with color.

For me, I'd need to have the plugs in hand so I could peer down there and observe the color ring and its position.

My only recommendation would be to find an old hand who has done this successfully long before the advent of oxysensors and AFR meters.

[blucille]

2words....gunson colortune....

[ibmiked]

2words....gunson colortune....

Yeah, yeah. Thankfully I've got one.....

And thanks Steve. Guess I spent too much of my youth reading a Haynes manual and staring at the spark plug page.

Mike

[blucille]

I'm no expert, I'll say that up front, but I would expect more similarities from plug to plug.....I can understand that today's crappy ethanol 'enhanced' unleaded fuels will change what plugs will look like, I believe you should be able to get more of them to look more like #3 or 4 or maybe 6

[1QuickS]

I use the Colortunes but only for idle mixture adjustments and mixture diagnostics. I don't believe they are good for much else.

[304065]

Mike, I'm all in with you in spirit but truthfully you have to have an LM-2 these days with one 02 Sensor in each muffler inlet. A fairly big initial investment but pays off big time.

http://forums.pelicanparts.com/911-e...en-sensor.html

[blucille]

again, I'm no expert....but the more I patiently spent time with my colortune, the better I was able to get my recently rebuilt 46mm singing the way they should. At first, I got them good enough that I figured I was done....all the popping eventually went away, except at transition from main jets to idles.....the, with a little more fiddling, and reading the plugs a bit, I even got the transitional pops to go away.

thanks Paul, thanks colortune....