I have a HPI G3.0 engine in a MT2 that's doing some weird things. When cold, it has plenty of pinch, but once warm, it acts like a worn out engine. It doesn't want to idle when warm, and once warm almost refuses to restart. I'm pretty good at tuning these engines, but I have never seen one do this before. Has anyone else run into this? It was used when I got it, so I don't know how it's been treated before I got it.
I'm planning on just doing a rebuild(don't have enough for a new engine) and starting from scratch, but would like to know why it's doing this. If anything, it wants to run overly rich once warm. I never let these engines run lean or with a lack of lubrication(if I don't see some smoke, I richen it up ASAP).
Thanks.

i new to rc cars but i did fly free flight airplanes in the past. sounds to me like you might have a small air leak. sealed when cold but when the metal expands you might have a air leak.
this has happened to me and it is hard to find. usually the back plate or around the carb. reseal them and see what happens. good luck hope you can find the problem. i hope this atleast heads you in the right direction.

I agree with the air leak prognosis. Heat up the engine with a heat gun and plug the carb and exhaust with rubber corks. While blowing on the fuel line to the carb spray the engine with a soap/water solution. Any air leaks will show up as bubbles.

Good luck!

Tore it down and think I might have found a major part of the issue. There's a deep scratch in both the piston and sleeve. Got it running pretty good for now by just removing one shim from the head during reassembly(came with 3 from the factory, so has 2 now). The new piston, sleeve, and conrod should be here Friday, so that should be that. Didn't do any sealing on the engine during reassembly, but it seems to be running much better. I did however apply some castor oil to all the bearing points and the mating surfaces on the back of the engine, as well as to the piston and sleeve(hate starting an engine dry).
Once I get the parts, I'll do the same thing, oil all bearing points during assembly, as well as on the piston and sleeve. Only reason I chose castor oil is that it's used in nitro fuels, so it should be good for startup lubrication for the breakin.

You could also purchase some after-run engine oil. After every run, I take the glow plug out and put a couple drops into the engine, and a couple in the carb, so it always is starting lubricated.

glad you found the problem have fun racing