R/C truck

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I have a Revo and a T-Maxx, do you have the manual? Set the needle screws back to factory settings and start there.
The Traxxas site has videos and manuals online.
Check the lid of the fuel tank for a good seal, if there is a fuel filter check that, if there isn't you should add one.
Turn it over by hand and check for compression, you can use soapy water to check for air leaks around the carb and backplate.
What percentage fuel are you using?
Use fresh fuel and probably wouldn't hurt to use the same % that it was run on before.
Did the seller say how he broke in the motor?
If you don't have any luck you can take it to your LHS and ask them to check it out.
If worst comes to worst Traxxas has an engine trade in program.
I'm converting a Thunder Tiger 4wd nitro Dodge Viper to a drift car and trying to figure out a place to run it when I'm done.