Originally Posted by porter

IN my experience the O.S. stock bearings have a reputation for not being the greatest on the market. Most engines will have a small amount of bearing leakage while breaking them in (Engine running on the richer side). Then generally the leaking will slow as your able to start leaning things out.

Mine leaked through the first gallon and a half but has since slowed or stopped all together. I have right a 4 gallons on my latest JX21 and will be replacing bearings shortly. It will have new bearings before our next nitro season starts anyway

If your not sure, it's never a bad idea to just replace them. Mainly for your piece of mind, and it can't hurt anything.