Originally Posted by
kmeyers
More is needed about your tuning. Are you a pinch test tuner? Are you a tach tuner? Do you tune by ear?
When you say as rich as possible what is the data (reasons).
How old is your fuel tubing? How do you store your fuel? What Prop are you using? What glow plug? Besides Aloha, where are you (weather conditions, yes one might guess)?
The simplest reason for leaning at a while into a flight can be a hole in the tubing, brass or line, inside the tank that becomes exposed as the fuel is depleted.
Try tuning with 1/2 tank, then fill it.
These are a few quick thoughts.
1.) I use a 13X6 prop for this engine (recommended)
2.) I usually tune by ear. I listen for peak RPM then back it off a little. After the engine kept overheating I really richened it up. I have tried several setting between just below peak RPM to just inside the threshold of two cycle operation (right after the transition of four cycle operation into two cycle).
3.) The fuel tubing I use is about three months old.
4.) I use a # 8 glow plug.
5.) Yes I am in Hawaii. Temps average in the high 70's to low 80's with approx 70% humidity this time of the year.