Topic: Hotter plugs to richen? Colder to lean?

[Knightro]

How can I temporarily richen or lean my mix without fiddling the carbs
Hotter colder to richen hotter to lean?

This is what it said in FAQ for carbs in this forum...     but it honestly doesnt make sense.   

Lean mix runs hot...   you want to add heat to that mix?  I know its not a 'fix...    its a bandaide.  But while i wait for my new jetting....  i'll take a bandaid.

[333]

It's a misconception that a change of plugs can solve jetting problems.  If you are running rich, and try a hotter plug, you can burn a valve or burn a hole in to a piston.  It is confusing, in that the plugs are the indicator of whether your jetting is correct.  More spark won't burn more gas.

[Dunk]

Indeed. Too hot and the plug can ignite fuel from its own heat rather than spark, or wear out more quickly from heat. Too cold and it will foul with soot easily. To select heat range you want the change in color of the ground strap (from heat) to be about where the bend in the ground electrode is.

If your engine is stock, use the factory heat range plug. If you have a high compression engine colder plugs may help avoid detonation when running the timing curve the engine runs best with.

[TwoTired]

The plug's heat range has to do with how fast the spark plug will wick heat away from the chamber and into the head.

NGK D7 range is slow to remove heat, making it a hotter plug with elevated burn temps.  This tends to allow the plugs to "self" clean off too rich deposits due to its hotter operating environment.

NGK D8 range wicks heat away from the combustion chamber faster and is a colder heat range plug.  A lean mixture tends not to overheat the chamber.

The 550 has a smaller head/cylinder mass, so is less likely to retain heat compared to the 750.  550 generally uses D7, 750 - D8.

Neither plug has the effect of actually changing the delivered mixture.  But, the plug deposit effect of a too lean or too rich mixture can be slightly ameliorated by changing the plug's heat range.

An old trick was to use a hotter plug to make oil burning engines foul their plugs less frequently.  Didn't "fix" the oil burning.  But, made the engine run longer between spark plug fouling events.

[Knightro]

Ok folks,

Thanks for the clarification, so, to reiterate, switching plugs may help eliminate some of the symptoms of rich/lean mix resulting in some maintenance/spark plug benefits, however; would not eliminate the performance issues running lean or running rich may cause and resulting long term maintenance/damage issues.

In the end, work on the jetting, get that tuned, run the recommended heat range plug.

Thanks all!