RC Cars/Trucks in "Off Topic" Posts Posted January 13, 2003 Breaking-in an engine seems to be the most controversial as well as the least understood thing in r/c cars. They know they need to do it, but there is no one true way to accomplish it. I'll just follow the engine instructions for now, couldn't hurt too much, if at all. XRW, yep, was the low speed needle. Richened it to around a 1/4 turn and it ran like a scalded dog. I still haven't got the idle right, but it's very close.