Can agree more with syco.....

second hand nitro's are very touch and go, there are some good ones but the majority are wrecks.

Same old story, they didn't know how to run it and and tune it, so they never did. Then they wonder why it won't hold tune, and has starting and hot running issues... Then they give up and sell there nearly brand new car with a motor that's been ruined within only a few tanks...

or or ur get the guys that think they know what they are doing and tune it for max power not releasing a nitro motor needs to be slightly rich for lubrication. Then the motor turns into a ticking time bomb, that will either snap a rod or wear out until it has no compression when hot.

just keep in mind nitro engine do have a learning curve. If u have someone to teach u the basics it can be less costly but self learning by mistakes can get expensive...
The hardest parts to learn is what should the engine sound like and how should the exhaust smoke look.
its like riding a bike, it can take a while to learn but u never forget.
Also for learning purposes it would be better to get something brand new so u know u have a solid starting point.