Recently when starting my engine, I've had to richen the low end about 1/4 turn more than it had been during the summer. I had to richen it even further today after a dryline came through and dropped our relative humidity to very low values. Is this normal? Do gas engines generally need richening in drier air. Also what about colder conditions. Does it need to be at a richer setting in colder weather than in warmer weather. Colder air holds less water vapor than warmer air.

Thanks,

Greg

What engine are you useing? You may want to richen up the idle and run the high screw a little rich. I don't think you should "NEED" to adjust the mixture during the season.

Cold air has higher density and more oxygen is going through the carb venturi. Needles need to be richer to flow more gasoline. The fuel to oxygen ratio has to be constant for best performance. However, it's usually not that critical within small temperature and humidity changes. As humidity increases, there is less oxygen going through the carb venturi, needles need to be set leaner.

Thanks,

That explains why I needed to richen it. The temperature is some 40 degrees or so lower than when I had been flying during the fall.

Greg

For what it's worth, My Zenoah G-23 was acting like that this summer. Never touched the needles before and all of a sudden I had to open the low and high needles several times. Turns out the fine screen filter in the carb was almost plugged up, and I was running a filter in line also. So keep an eye on that filter as well.

Anytime you have to make a a large adjustment to the needles, there is a problem elsewhere. Air leaks, dirt in the system, etc.