Haven't replied since I didn't want to hijack the thread into a "how to fix your RCS 140" one, but since you replied... I looked carefully at the options, and it seems to boil down to the EVO as the only engine in the power class that will not require further cowl modification. I eliminated the First Place 1.3 because an owner pointed out just how much less power it has (about half).

I followed Milton's advice and decided to take one more stab at the RCS. I pulled the carb, checked the lineup of the pulse holes all the way through (all looked OK), checked the shim which seemed to be reasonably straight, and then put a coating of Hylomar on both sides of all three gaskets, and reassembled it. Spent another half hour messing with the needles, and while I could get a reasonable transition in both directions, I still can't get it to idle below about 2600 reliably. I'm going to try to fly it this weekend and see how it goes, before I make a final decision.