Hey Randy,
I was going to call you about this but decided to ask the question here so maybe other folks could benefit from the answer also.
I've recently put my PA61 SE in aKA10 (look alike)...I actually had a Double Star 61 RE lite in it first and couldn't get it to work...tried just about everything in my bag of tricks (which actually is substantial) but nothing worked...Sooooo...Shoe horned in the PA61 and boy oh boy did that wake things up...Nothing like POWER!!!.
There is one little thing that is happening that has me puzzled... It's not a real problem but is mysterious (at least to me under these circumstances.
Incidentally this is the 61 I got from you a number of years ago that you was running in one of your airplanes.  I needed one and you graciously yanked it from your airplane and sold it to me.  Its always been a terriffic running engine.
However...to the problem.  It gets slowly richer through out the flight.  Not so much that it's a real problem but it is a little disconcerting in big wind to not have quite as much on tap near the end of the pattern for overheads etc.
If I was running a pipe I would certainly know what the problem was and could fix it in an instant....however no pipe.  I'm running a tube muffler with no pressure and a uniflo wedge 6.5 oz tank.  I've checked all the standard things no leaks anywhere in the exhaust system or fuel system.
Is it possible the tube muffler is acting like a very short pipe and causing this?   I'm going to try a tongue muffler but there is a contest here next weekend and I hate to keep changing things to the last minute. 
Any Ideas?

Thanks,
Randy Cuberly

Hi Randy

That is not typically caused by the engine, 99% of the time that is either from the fuel system or heat. First thing I would do is to change tanks, and check to make sure I had good airflow thru the cowling.
Also make sure the motor or any exhaust is touching the fuel system anywhere

Regards
Randy

Randy,
Thanks for answering so quickly.  I have changed fuel tanks and pressure tested everything including filters and fuel lines.  The airflow through the cowling is very open with no restrictions past the engine and at least three times as much area on the exit as on the entrance.
  I really hadn't thought about the engine heating the fuel but it's possible.  I'll check and see if I can insulate the tank from any wayward engine heat.  Certainly, I'm flying in 100+ degree heat.  Someone here suggested that 22% was too much oil and could be causing it but I've never had any problem with my other PA engines on 22% oil and 10% nitro.
Thanks for the suggestion, I'll let you know what I find.

Randy Cuberly