When you richen the nitro engine's mixture you're adding more fuel than air to the nitro engine. This rich mixture can give you better results for some kinds of races because this method, unlike leaning out (more air), will give you cooler engine temperatures. But if running too rich you can not only bog the engine down and stall out but also flood it and foul the glow plug.
A rich mixture may be called for when:
- the engine dies while idling;
- you don't see a light stream of blue smoke from the exhaust;
- the engine overheats.
You may be running too rich if:
- there is too much blue smoke from the exhaust;
- there is a lot of unburned fuel from the exhaust;
- you can't reach top speed.