The Saito 220 is running better now, transitions good from all rpms with only a 1 sec slow down, even after extended periods at idle (or any rpm).

The intake insulators did the trick for stabilizing mixture settings at varying engine temps but did not fix the lean cough condition during transitioning.

Here was the major culprit:

This tank is very flimsy. During transition too much of the muffler pressure supply was being used to reinflate the tank instead of applying additional fuel pressure. Swapped it for a rigid 16 oz Dubro tank and things immediately and drastically improved. I was able to lean the mixture from those overly rich ones I was forced to use with the flimsy tank. The engine temps decreased too, as expected.

But all is not well. As the fuel level depletes, leaving more compressible air in the tank, the transition problem (lean coughing) returns, although not as severe as with the flimsy tank. The engine temp rises very quickly when repeatedly transitioned under those lean conditions, as expected, which exacerbates the problem. With 3/4 to a full tank of fuel the transition is rock solid. I was ready to lob the engine into the Taylorcraft, that is until the tank level dropped below 3/4 full and the problem returned.

I'm still convinced that the fuel system needs more pressure, some how, some way and here's why. The engine now never misses a beat transitioning when above 5000 rpm and it doesn't matter if the tank is full or near empty. 5000 is the rpm where the muffler begins providing a higher and exponentially increasing pressure. Below 4000 the pressure curve is flat, essentially not changing much from idle to 4000. To transition these big Saito singles appear to need big fuel and in a hurry.

In the meantime I'll try a smaller tank, a 12 oz. The smaller tank may help, if for no other reason than to prove a theory.