Originally Posted by Rapid Roy
If you are retuning, richen up by 1/4 turn or so if your engine was tuned correctly previously. One full turn is wayyyy to much. You adjust 1/16 or 1/8 of a turn at a time, running the car as close to race conditions as possible for at least 2 minutes between tweaks. Bring the car in and read the temp right at the glow plug immediatly. You can tune for maximum performance while keeping the temp from going too high by doing this. Just keep in mind that running on the ragged edge will require you to make on going adjustments as the weather changes. If you tune a little conservatively you won't need to make as many adjustments at the cost of a bit less power.
There is now magic temperature. Each engine is different and barometric pressure, humidity, fuel mix and air temp will change the temperature the engine will run best at. The temp gage is only a guide. Check out the TZ thread in the engines forum for some good guidelines on temp ranges.
Going a full turn richer on the top I meant for a used engine that you dont know its history. 1 turn does seem excessive but it is better to be safe. It is easier to lean a blubbery engine than richen a dead one. I should have clarified this in my original post. Rapid Roy has got it on the money a lot clearer than I could. It is a lot harder to type what to do than show someone. Goodluck with it.