Since new the U2 has had a terrible cold start up POP POP POP POP POP POP. .. POP…POP!!!! and POP!!!!! It required a long long long long long warm-up.
I have been told, and the research confirms, that the carburetors are set extremely lean to meet US emission exhaust standards. This weekend I put a CHT gauge on the rig and determined that the cylinder head temperatures needed to be at or above 300 degrees F before the popping would calm down.
That was just not tolerable. So, I got a carb jet kit from Holopaw.
(http://holopawcorvette.webpointusa.com/): Mains: 130, Pilot (Idle) 45, and 8 SS allen screws:

My research:
http://myural.com/keihin_32cvk_disassembly.htm : carburetor parts
http://www.dwightrahl.com/carb-jetting.html
http://sovietsteeds.com/forums/viewtopic.php?t=324
Changing the jets was easier than I thought it would be. Took about 30 minutes total time. I just loosened the hose clamps of the carb flange and air filter intake hose and turned the carb upside down, leaving all other attachments in place. I followed the instructions above. I took off the bottom float pan and screwed out the jets, then replaced and reassembled. I took some pictures, but go to the links if you are interested, there is much better documentation.
Guess what? A HUGE HUGE difference! Only a couple of small pops and puts when coldest to remind me to let the thing warm up a bit before blasting off. The jets that came out were smaller than advertised. The main jet was only 122 (thought it would be 125), now 130. The pilot (idle) jet was 40, now 45.
Happiness is a modification that works!
I should check the plugs now after some more riding time.
Now, what about those catalytic converters?