I would say sell the one you have and get a new RTR brushless setup and save yourself all the headaches;-unless you like what you're running that bad..
I found that if you take the time to disassemble the engine and carb,clean them up and reseal them properly with new seals and o-rings you can eliminate the obvious problems to why the engine wont tune right....The obvious problems are worn out engine, air leaks at bearings,carb slider/rotator or carb needles or clogs and dirty needles.The others are faulty glow plug,glow starter and improper tuning practices..There is a vid running around u-tube on how to check for leaks by only removing engine from chassis and using bubbled soapy water with a brush.Try removing the tank,washing it out,removing the engine and resealing it totally,adding new fuellines and new cleaned-out fuel filter...Start out with factory carb settings,fresh fuel and new glowplug thats right for the engine and ambient temp range..After that it should either run and tune right or its junk and needs a rebuild or replacement.. Good Luck