13
$\begingroup$

I was reading the DLE-120 engine User Manual and saw this paragraph:

Caution: Running the engine with a lean fuel mixture will cause the engine to overheat and burn the electrode of the spark plugs. Pay close attention to the High-speed Needle adjustment. Running the engine with the proper fuel mixture will make the spark plugs appear yellow at the ignition point.

What does "yellow" mean in "Running the engine with the proper fuel mixture will make the spark plugs appear yellow at the ignition point"?

Does anybody have any experience or images of this phenomenon?

$\endgroup$
27
$\begingroup$

Use the tip residue to evaluate the combustion process

The yellow the manual is describing is the normal condition found in the top left corner:

enter image description here

If the plug is not the yellow/tan shown in the top left, then it will almost certainly look like one of the other pictures. This is a strong hint that what is going on inside the cylinder is not optimal, and points in the direction of the problem.

$\endgroup$
2
  • $\begingroup$ Thank you for your perfect answer. another question: Is this colors valid for piston engines which use fuel+oil or it is valid for piston engine that use just fuel like car engines? $\endgroup$
    – Roh
    Mar 29 at 12:55
  • 2
    $\begingroup$ AFAIK, it is valid for both. Be aware that some of the remedies make less sense for a fuel/oil mixture, though (such as checking piston rings for blow-by due to oil fouling on the plugs). $\endgroup$ Mar 29 at 13:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.