More Tech-Tips - Tech-Tips2
TECH-TIPS #2 of 2
Aug 1997 TFRB
Reading Spark Plugs
Looking at the white porcelain part of flathead's spark plugs - after it has run normally - can show you how the Heat-Range of your plugs is:
If it appears very white, perhaps with small dark spots, it may be burnt - Too Hot!
If it appears oily - it may be Too Cold!
The Electrode can also tell you much the same.
The color of the porcelain will also tell you how the fuel-air mixture is:
It should be a very light, just barely brown.
If it appears very white, with no color, it may be Too Lean - not enough Fuel mixing with the Air - needs bigger jets.
If it is medium to dark brown, or sooty it may be Too Rich - too much fuel mixing with the Air - needs smaller jets.
If it appears wet or oily, your rings may not be controlling the oil past the pistons. This is also usually obvious as the exhaust smokes a bluish color.
Here are 2 good sites to see how to do this, with great colored pictures: WikiHow/Read-A-Spark-Plug YourMechanic/How to Read a Spark Plug
Sep 1997 TFRB