It has a standard - i.e. non-insulated - carb.

I have had the LRP Spec 28, the Losi 454(same engine), and a bunch of other engines from the same factory. They are all great. But...., they don't tend to idle perfectly. I learned to live with that by blipping it to clear it out. Oddly, my 454 purrs like a kitten... But a lot of how an engine tunes has to do with fuel, plug, pipe, and how the owner tunes it. I tend to like mine a bit rich on the safe side, but still with a screaming top end. Anyway, the standard engines are great for the money. The ZR.30X though has a much better carb. It'll just sit there and stay idling. It's very easy to tune, and keeps a tune. I've come back to mine after six months of sitting, and it runs just fine. To be fair, I can say the same about those other engines as well.

So I don't know. All I can say is, my ZR.30X has been an absolute BEAST in terms of power, and the tuning side of it is just really good, more like a Novarossi or other race engine, which will sit there and just idle steadily.

ps You can get those other engines to idle steadily too, but IMO you tend to have to use a hotter plug, and for me anyway when using a hotter plug (like an OS 8 instead of a 10), I notice a drop in top end power, revs, and speed. BTW, the Odonnell purple medium plug is the BEST non-turbo plug you can get for MT big blocks...