I recently ordered one of the new Great Planes Dirty Birdy's and planned to power it with a Webra .61 Speed that I picked up on the auction site. I particularly wanted this engine because of the other two Webra .61 Speed's that I own, this is the only one that was factory-drilled for a bolt-on muffler. Well I haven't found a Webra muffler yet so I ordered the Mac's generic muffler and an aluminum bolt-on adapter. All that works as advertised, but found as I finished putting the Dirty Birdy together, that the spinner adapter I used for my other Webras won't fit this Webra. The others are a 1/4" thread, this one is an 8mm thread. Can anyone explain that?

ChiefK