This bike runs great up to about 10 mph then engine starts to skip, now using 90 octane ethanol free gas.  Feels like a carburetor problem but have cleaned every inch of carburetor and adjusted the air screw.  Appreciate any help.
Thanks.  

Pull the baffle & try it. Will be noisy. Could pull the air filter unless ya sure its good & not falling apart. My HT1 pulled 55mph on a racetrack all day long. Depends what you mean by skipping though. If the mag is a bit weak & points a bit dirty plus plug gap too wide then yes you'll get an electrical misfire which could be described as skipping i guess. Misfiring it instant missing where blocked exhaust is more restricting performance to a limit but a gradual limit rather than a cutoff limit. Hope that makes sense.
ps, gap alters timing but i'm thinking if its out past recommended max of 15 then timing is likely a bit early anyway & wide gap will cause misfiring, not the early timing exactly. Conversely  if the points are barely opening from fiber heal wear then it'll be way late on timing & kill the performance but probably not misfire, just flat power.