I have a gx21 in a new inferno mp7.5 rtr. Bought this as a intro for my son to get into nitro but i am having trouble with getting the engine to keep running on breakin. I was on the first tank of fuel and the engine would keep running for about 3 minutes. Would run fine for a while but then the rpms increase and the wheels spin and wants to take off. Just cant seem to find the sweet spot to keep the car running. Since we now have a thunderstorm that moved in I thought id try and get some expertise from someone on here till I can start tomorrow. Kyosho's instructions for breakin suck so I am just trying to play the idle on ear but still not working. If someone could help maybe with needle placements or any kind of suggestions it would be great

Quick and high rpms means its running lean. If its while the throttle isn't open much especially at idle richen up the low speed needle. If its past 1/4 throttle richen up the high speed needle. You could also have an air leak. Check the seal around the fuel tank cap, loose carb or the main needle valve is loose where it screws into the carb, or a hole in your pressure line to the fuel tank.

hi,
You problem you need to check this three point
1.- Please take off the air filter and check how many space you have in the carb in the neutral position. They need to have 1.5 mm or 3mm. Depend you location.

2.- Little Stampy explaind very well this point. You running lean.

3.- The last one have less probability, becasue you car is new. Check you cluth shoe and spring. The effect of "the rpms increase and the wheels spin " is because something is obstructed teh clutch shoe or srping and they quick expand. Another reason is because the nut screw of the flywell is adjust too hard. And the last one is because the clutch shoe or spring is too light.
Really this case is the last option to check.

Note:
Please dont try to adjust the three point togueter.