Hi Paul,

To answer your two questions:

1. Yes, when you dive, then engine will pick up rpms. This is normal.

2. Temperature and pressure will have an effect on the mixture settings. When it is warm out, the air is less dense. As a result, you need to reduce the amount of fuel in the mixture by leaning out slightly (ie. turning the high speed needle 'in'). When it is cold out, the air is more dense. You will often need to richen the mixture (ie. turn the needle 'out') to compensate.

Our club does flight instruction on Tuesday nights, and I've definitely seen a trend where most of the planes are running lean on cold evenings, especially if the previous Tuesday was warm.

It is good for you to be concious of whether you are running lean or not. The majority of trainers are well over powered, so it's not necessary to lean them for maximum power. If you are not sure of the 'right' setting for the mixture, go ahead and leave it a little rich.

One quick test of this is to run the engine up and pinch the fuel line to the carb. If the rpms drop off and the engine just quits, then you are too lean. If the rpms pick up dramatically before they drop off, then you are too rich. Ideally, you want to hear a slight pick up before the rpms drop off. That should be about right.

I hope that this helps,
-Wade