For an Acme 1/10th model:
With the radio equipment off please do the following
1. First of all open the carb so it is fully open. Look down into the carb and you will see the tip of the low end needle. If you adjust the low end needle you will see it moves this forwards and backwards. Adjust this so that when the carb is fully open the very tip of the needle is 2mm away from the tube it slides into.
2. Now close the carb as much as possible and it should still be 1mm open. If it is more than 1mm open you need to adjust the idle screw a little anti-clockwise and try again. Each time you adjust the idle screw you will be able to close the carb more. You don't want to do it to much though or else the carb will close completely which will cut the engine.
3. Next adjust the main mixture screw so the top of the screw is about 1 - 2mm below the top of the screw casing.
4. Use a hex wrench to make sure the screws holding the manifold are on tight.
5. Use a hex wrench to make sure the engine head screws are tight
6. Use the glow plug wrench to make sure the glow plug is quite tight.
Manually open the carb to about 2 - 3mm for starting and then when it starts put it back to how it was at about 1mm. If the wheels still spin quickly turn the main mixture screw a quarter turn anti-clockwise and wait a couple of minutes. Every time you do this it should slow the engine down a little but the changes take a couple of minutes to work so you have to be careful of over doing it.
That's it really. If all is done as above it should work.
For other nitro models there may be some slight changes in settings but the basics are the same.