Ed Anderson wrote:

I certainly agree with Tracy.  Get to know every nuance of your engine.  How it feels, what the vibration is like, what does it sound like at 3000 rpm, how does your EGT respond to throttle movement, what does the exhaust drone sound like, etc.  I must admit I haven't sniffed the intake air, yet - but, I'll try that next time {:>).

Absolutely, Ed, And after 60+ hours I DO know a lot of the nuances of the engine. What seems hard to discover is what to do about the nuances when they're wrong.

Tracy said:
I suspect there are a lot of clues to what is wrong other than the 'splutter' at 38".  
We just don't know what they are.

Right. Thats the problem right there, and as one of the uninitiated, I'd love to know what those clues might be.

To answer a couple of other questions or points, as I said in my earlier email, the engine ran fine after it cooled down. The symptoms reappeared during the take-off run.

The plugs I'm using BUR7EQ/BUR9EQ don't allow for gap adjustment.

John