That is very true, but before assuming that the glow plug itself is bad, it is a good idea to try and see if you can get the engine NOT to change RPM's when the glow plug is removed, by leaning the low end even more.

Also poor fuel flow or lack of muffler pressure can cause the same sympton.

Going the other way, the Evolutions are famous for their "grey goo", that consists of metalic particles which wear off of new engines.

This can foul the plug and can be the cause of the need to change it on a newer engines.

Usually the "Grey Goo" condition disappears after a few gallons are run through the engine.

The goo can also clog the muffler pressure nipple, so clean it frequently with a small hex key, particularly when the engine is relatively new.



One note:

The Evolution engines come with "long" glow plugs.... that are very similiar in length to four stroke plugs.

This is what the manufacturer uses.

O.S. A3 plugs will work but they have a shorter length.
This can affect inverted mount engines, particularly during startup attempts.