As kangaroo and downunder have already indicated, many bushing engines can and do develop a little rattle at low idle. No worries. A few years back we had a going little event for pylon racers using the K&B .28 Sportsters a delightful little engine known locally as "Teakettles". You know what, the noisiest of the teakettles were always the best engines and tended to always be the winners!

I still have some of those nifty little teakettles going strong fifteen years latter.

John