First off, aluminum really likes filler metal. Even just puddling for practice beads needs filler.
Second, soot can come from lack of, or bad gas, as well as contamination on the base metal, filler wire, and/or electrode.
Third, for 1/4" aluminum i would want a good 250 amps available on the pedal. Don't have to use it all, but it helps to get going.
Correct me if im wrong here: The syncrowave's AC balance is a 1-10 dial right?
If its the one i'm thinking of '0' would be 55% EP and 45%EN. 😬
Try setting the Balance to '3' and let it simmer to see if it gets shiny.
Then try Balance of '10' and do the same.
Can you find any aluminum that is of known alloy?
That wheel my not be what you think it is...some aluminum alloys contain Zinc, Lead, and other nasties...If it stinks, STOP!
Make sure your gas flow is appropriate for the cup size.
Max cleaning may be toasting your electrode and giving you issues.
Long story short...Up the amps, Up the Balance, put on a respirator.... and call me in the morning.