Nelson glow is on order. But to get any idea what temperature I shoud keep, I did some measurments.

First I measured the resistance of the glow plus (OS F long) at different temperatures. Unfortunately the IR thermometr I had (from Harbor Feeight) didn't see the glow element properly. So I tried to get the temperatuire based on the color of the glow. Then I realized, that I don't need to know the temperature as long as I know what is the resistance corresponding to the full powered plug (glowing orange).

Because the resistance of the glow plug is minimal I used piece of steel wire as a regulated resistor connected in series. This way I regulated the voltage on the glow plug and reading the current I I used it to calculate the resistance. See below of teh graph of the resistance versus voltage, and it is quite linear, so the temperature is linear to the voltage applied.

At the full power (1.1V) the glow element is orange and the calculated resistance is about 0.37 ohm. Now I run my engne with the glow plug regulated through the same wire. I measured the volatage and current on the glow element calculating the resistance, that should directly indicate the temperature. See pictures of my setup below.

I coludnt't get exact result as the engine was not running well - I didn't tune it well after running gas-glow fuel the last time. I did rough adjustments to the carb so I got reliable idle around 2000 rpm and full power at 7200rpm - the same results I got the first time with megneto. I don't need to add that I'm running gas-oil (40:1) only - NO METHANOL. The engine was not running smooth - it still needs more fine tunning.

Now I was so surprised, when applying normal power to the glow plug (1.1V) when engine was idling (2000rpm) I read current 2.2A. That gives over 0.5 ohm that translates to over 1.3 times higher temperature of the orange glow. It is when engine was idling. I didn't get all data (what current the glow plug will get the temperature corresponding to the orange glow (0.37 ohm) and if it still runs smooth) because I tried to tune the engine for smooth run. However I got the measurment at half throttle when the engine was still running without noticable dropping of rpm. It was 1.8A at 0.88V what reads 0.49 ohm but I believe after tunning the engine I will be able to get it running at the lower temperature.

I will try to do it next weekend, but I will go to our flying field - backyard is not a good place to run weed-whacker engine without the muffler