sintoms> the engine starts at idle but when i open the trottle it stops ,( no is not lean)tryed to open or close the needle, cleaned the carb ,no result at all.Then I cheched te plug it look PERFECT(i refer to the shape of the coil)the plug is a R 2 that worked good on my os 1.60.I tryed to change the plug with an os 5 the engine is now running good. I can not understan why a plug that look good can give so much troubles.When i had these prob I was using cool power 15% instead 0% nitro and 18% aerosave can a change in oil/nitro be the explication?

How do you know it is not too lean?

ampa,

Sometimes a plug can look fine, glowing fine when you put the driver on it, but still be bad. Since a new plug solved your problem, just throw that other one away, and remember your experience in the future.

Plugs sometimes get a coating on them that renders the Platinum useless and the catalytic reaction no longer happens

Ditto!
plugs are like sparkplugs. If they stop performing, toss them, do not put them back in your flight box.

I had the same problem, a club member told me that plugs can "grain" over time, meaning that deposits form on the surface of the platinum giving your symptoms.

I threw my duff plug as far as I could. Luckily no one else has found it to use!

I have had pretty good luck with soaking dirty glow plugs in acetone for a few days and blow then clean with about 100 PSI of air. Use a small glass jar...you will see the oil ...ect come right out. Capt,n

yeah ive seen that on OS #8s , it kinda looks powdery white, perhaps some kind of corrosion or due to extreme heat or maybe even a lean run or two

You can throw that plug in the flight box for a few months and then it will work again

ampa,

There is another, maybe "forgotten", story to tell.
I did not read this in the other posts I thought.

In the past we successfully did use glow-plugs with a bridge.
The cold mixture from the crankcase, maybe still with real particles liquid and so not evaporated completely, can blow down the plug temperature by evaporating ‘on’ the wire.
This is called, “latent energy absorbed during evaporation�

This has also to do with the tank lay-out, environmental- and engine crankcase temperature!!
For that we did use the bridge to screen the wire of the plug.

Even the trick was to mount the bridge (yellow) in the flow direction (blue arrow) of the gas stream by adjusting the gasket thickness!!
The blue arrows are pointing to the exhaust in that situation.

I myself always have a loupe to observe the plug wire!

Most important advice, always wait untill the engine has a normal operating temperature.
I normally run the engine on a little higher RPM than idle for a while to get a higher crankcase temperature.

Cees