I have been trying to tune for the cold start for a while. I live in MT and we have had a lot of sub zero temps this winter.
Your cold start sounds pretty typical for the stock 22R carb. As much as I like the Aisan carbs I will admit that these things are cold blooded. Mine is freshly rebuilt, fairly clean and all the cold start features are working. I usually have to let mine fire once, sometimes twice before it will keep running below freezing. It will keep idling kind of low at this point and in about a minute or two I can drive away.
Usually I pump the pedal twice, then it fires and dies. The second time, I pump twice and it fires and may or may not run that time. The third time I usually always get it going, however, if I push the gas pedal it at all for the first 30 seconds or so it will die.
The HAC probably won't help with the cold start but it would be worth running if you can find one just for dealing with the altitude.
I would start by setting your idle mixture per the manual. Turn your mixture screw all the way in to the shut position then back it out like 2 1/2 turns. It's OK to adjust your idle speed screw to crack the butterfly just a bit to get the cold start. This sometimes helps and basically gives you a slightly open primary. You don't want too much, just a bit. In winter tune mode I like my warmed up idle at about 1,200 rpm. This will be a balancing act between idle mixture, idle speed and ignition timing. This position seems to like to start better.
You should probably check to see if the choke is doing what it is supposed to. This is the plate on the carb located on the drivers side on top of the secondary. It should be closed on startup then slowly open as the engine warms up.
I have also had good success advancing the ignition timing a bit for winter. This might make it so you can't run on 85 octane any more but it helped me get the cold start.
It never hurts to rebuild your unknown, old carb. I would do it when you get the time.
On other thing I have learned is that it seems to help the cold start if you run a little bigger main jet. I started with a 112, then swapped to a 119, now I run a 116 main jet. The fatter (richer) main jets seem to cold start a bit better. If you don't have any carb laying around to scavenge jets you can use Hitachi main jets. They are the same size and have the same number system as out Aisan carb main jets.
I ordered a 116 from these guys a while back...
http://www.jetsrus.com/a_jets_by_carburetor_type/jets_hitachi_main_4H7.htmlOne more thing. I have had good success running thinner oil in the winter. I was running 5W30 and that was better in the cold than 10W30, but I recently switched to Mobile 1 0W40 and it made a large, noticeable difference in the cold start. I got it on the second bump this morning at 18 degrees. At 10 below F it will still start after a couple bumps of the starter. At 20 below it will still do it with some effort but the block heater is really nice
.
