Remember that the Pilot screw is an air adjustment screw on the TM38 as it is on the air filter side of the carb. As you screw it in, you limit the air thereby enriching the idle circuit. I found with my Hall pipe that removing the rear plastic gives me direct access to adjust the circuit. I bought my TM38 from Jerry and had him modify it, so it already is close for my setup. I had a 30 on my bike and the RPM hung a little like your describing at about 1 turn out. I screwed it about all the way in and it became so rich that it smoked like crazy and started loading up. I changed to a 32.5 pilot, but my air screw had to be total out of about 1 turn to be correct riding at Glamis in the winter.
I just bought a 35 pilot and plan to install and tune that one on my bike. If you can at all, I would suggest moving the Elka reservoir at least a little so you can adjust the pilot air screw without having to turn the carb.
Good Luck.