EGA and plug color...

[Mike Hart]

I had a very interesting time at the local Moto-Guzzi shop, they deal Aprilia and Laverda also - Moto International "cogito ergo zoom"

They have an exhaust gas analyzer, and use it a lot. As Ken D. pointed out in another thread, it's only good for idle and off-idle, as higher rpms are pretty much meaningless without a load on the engine.

At off-idle (2000, 2500 rpm) the EGA says I'm right on the money. At idle, a tad lean, just a bit, turning in the idle screws just 1/4 turn made a difference.

What was interesting was that the seemingly knowledgeable wrench there said he could never figure out why people tune for plug color, that when you use the EGA, when you get it in the correct range, the plugs are almost always white. He says he only uses plug color as an indicator on two strokes, that a perfectly tuned 4 stroke motor should have white plugs!!!

So, I learned something. Problem is, I don't know what I learned

Did I learn a new (to me) fact, or did I learn this guy is full of baloney?

Input and comments, please?

He says that without any lean symptoms (no surge, goes to redline) the only way to get any better is to go to the dyno.

[Bill]

Re: EGA and plug color...

Mike Hart wrote

At off-idle (2000, 2500 rpm) the EGA says I'm right on the money. At idle, a tad lean, just a bit, turning in the idle screws just 1/4 turn made a difference.

If you were lean, shouldn't you have turned the pilot screw OUT, rather than IN?

What was interesting was that the seemingly knowledgeable wrench there said he could never figure out why people tune for plug color, that when you use the EGA, when you get it in the correct range, the plugs are almost always white. He says he only uses plug color as an indicator on two strokes, that a perfectly tuned 4 stroke motor should have white plugs!!! He says that without any lean symptoms (no surge, goes to redline) the only way to get any better is to go to the dyno.

So, I learned something. Problem is, I don't know what I learned

• Did I learn a new (to me) fact
• or did I learn this guy is full of baloney?

I've never worked on 2 stroke engines, but EVERYTHING I've read about plug color on a 4 stroke says that

• The plugs should be tan when the mixture is correct, and
• White plugs indicate a lean condition

To quote from a Clymer's manual,

NORMAL

• Identified by light tan or gray deposits on the firing tip
• Can be cleaned

OVERHEATING

• Identified by a white or light gray insulator with small black or gray brown spots and with bluish-burnt appearance of electrodes
• Caused by engine overheating, wrong type of fuel, loose spark plugs, too hot a plug, or incorrect ignition timing. Replace the plug.

Interesting, but it doesn't directly mention a lean condition. Hmm?

[Dennyz]

Mike wrote:

"Did I learn a new (to me) fact, or did I learn this guy is full of baloney?"

At the young age of 14 when I first started drag racing V8 engines, plug color was the indicator everybody was using to fine tune their jetting. I have an old Chevy hot roding book that shows Smokey Yunick checking plug color on his race car.

Now, there is a difference between tuning for MAX power and Max fuel economy (either one could be considered perfromance).

It would not surpise me if most modern cage engines run with white plugs for two reasons. Fuel economy and emmissions. A white plug would indicate that things are burning very hot, which is good for emmissions in these FI high tech motors. If the motor is design for this, it would OK.

The other factor to consider is the XS motor is air cooled. It uses fuel to help cool.

That's my $.02

[Mike Hart]

whoooooaaaa, Rocky, Mr. Peabody and the Way-Back Machine!! Smokey Yunick, far out.



Okey dokey, I agree about max power vs max economy. If I had a 4-into-1 I could put an O2 sensor in the collector and get an air/fuel ratio led display and know exactly what up at any throttle opening and any rpm.

In those terms, I think 13:1 is about right for max power, and 14.7:1 max economy without being too lean. I'd like to be at about the middle of that

I don't normally redline the ol' XJ much anymore (that's what my Bandit is for), so I guess I shouldn't be too worried...but still, I think I have to jet up a little more.