The reason people try the OS carb is because many people have found out that they can't keep the Tigres running in the air. There is something peculiar about the ST3000. A buddy had one and we tried all of the recommended procedures (10% oil fuel, 18% oil fuel, FAI fuel, 5% nitro, 10% nitro, OS-F plug, Fox plug, stock carb, various prop sizes). His would quit about 2 or 3 minutes into the flight no matter what or how rich or lean the needle was set. I also know there are other people that have good running ST3000 motors. I suspect there are some quality control issues. Some claim that there are motors that went out with an unusually small ring end gap. When the motor runs for a few minutes it will seize. We didn't verify this theory with my friend's motor because he got rid of it first. I'm not new to motors and have never come upon one that I couldn't get running correctly until this ST3000. I also had to struggle with the ST2300 (like so many others did) to get that motor to perform right. Everyone now knows that the ST2300 problems were caused by a screwed up midrange metering system on the stock ST carb. A Perry Mega #5001 carb fixes it, as does an OS carb.

So you see, the factory engineers don't always get it right, or someone else may make a mistake on the production line and substitute the wrong part or machine it to the wrong dimensions.