I have had 6 STS engines and the only one I had problems with is one modified by RBmods. Right now I am running a STS D21T MKII. As a budget engine I think the STS D21B is one of the best for the money. I have a D21B that has WELL over 5 gallons on it and is still running fine. Like any engine a lot has to do with how you tune and take care of it.

In order to get my STS engines to perform like I want they run between 250 and 270 degrees. But in my opinion anything between 220 to 280 is fine. I run Byron 30% with a hot plug.