Need help with rc nitro engine

Sabrinalea

Hello I have problems with the breaking in of the engine of my new nitro rc. The first tank runs through without problems. But now on the second tank he starts to make trouble. The engine accelerate massive by it self and stalls after a few minutes. And on top the carburetor don't slide back into the idle position when he has moved.
Thanks for your answers and help

coolwings

I am unsure from your description whether the throttle settings are correct or not.
With the filter off, and looking into the carb opening from above - if the radio throttle stick is at rest, without contact from hand, the stick should be at 1/3rd to 1/6th from bottom to top. The carb opening should be 1/6th of a full moon open visible.
if not adjust the radio adjustment (beside the stick or throttle trigger) or the tops of the servos on the car so that the above is gotten to.

That is saying that hands off, upon starting the engine should "want" to run at a fast idle, not a race speed.
Assuming it runs faster than that, the tuning is wrong.

Fuel nitro content applies here as to diagnosis. Assuming that the fuel is suited for running in ....

A too fast engine is getting too little fuel, sounds wrong but it the case. Less fuel = more air = more oxygen inside the engine = more speed. We speed up by opening the carb to let more air in.

So usually the fuel is restricted in some way if the engine races upon starting so that it goes into gear and tries to drive off.

Unscrewing the main jet adjustment on the carb assembly, usually a tube sticking up with a screw in it, lets more fuel in. That should slow the engine down a bit making it more manageable. Too much lets lots of fuel in, drowns the glowplug and cuts the engine. Unscrew in 1/4 turn increments, taking notes if you're new, so that reinstating is possible if it doesn't work.

The engine revving up by itself is caused by overheating. The above adjustment should resolve this by cooling the engine down a bit (more fuel contains more oil which comes out the exhaust taking heat away with it). But a lower nitro fuel would do the same without changing settings.

Many descriptions are laid out without much understanding of what is going on, and when eg "Step 4 fails to make things better the user is left wonder what's going on.

There is a design flaw in many cars. Where the fuel tube from under the fuel tank is over-long, and the excess tube goes up and over something in a big loop. That impedes fuel flow, leaning the engine, causing overheating. I always pull the fuel tube off the carb inlet nipple, clip off the excessive length leaving only eg 6-10 mm spare, and replace it on the carb inlet nipple. This makes a host of problems go away, and yet still I see brand new cars with fuel tube far too long.

There is sometimes a second carb tuning screw, in advanced carbs. this smaller screw might be present at the side of the carb opening, going opposite to the feed tube visible looking in (if it's fully open). Don't play with that. It's factory set and even with experienced users only one in 30 can get it right. the reason is that it has no right setting until after the engine runs in and loosens up, so it's a best compromise while new, and that's takes a bit of experience to guess best what suits it.
If a fine tuning screw is already adjusted away from factory, read the book to see if it gives standard setting (Usually screw all the way in, then unscrew x revolutions).

Hopefully this helps. Best of luck.