I just worked on an H for a guy about a month ago. I cleaned and put a kit in the carb. After making adjustments by the rebuild kit instructions it did not run well either. I took it apart again to make sure all passages were clean and I got the throttle linkage in the slot right. Then I checking plugs, points, valves and timing. I ended up playing with the mixture and main jet screws a 1/4 turn at a time until I got it running right.
Hope this helps.
Rodney 8)