Hi jbspeed!
230Volts??? It's got to be a lot lower closed circuit voltage than 230V!!! :) :) :) More like 23-24 VDC!!! :) :) What's your gas flow rate??? Bring it up just a bit because of the increased gun distance from the work, but not too much... maybe 5 cfh more should work fine for you
Okay, 520 just a tad high but, I may be mistaken... If you can get it to weld with a good sized nozzle to work standoff distance, then you may just be within the ballpark so to speak... Now, what you need to know is with your gun, you need to have a CTWD (Contact Tip to Work Distance) of around 1/2 to 3/4 of an inch because if you're too close to the work, it's going to burn back and ball up on the contact tip... So dial down your burn back control down to zero, then increase your CTWD to 1/2" - 3/4" and start welding... If you see a bit of wire coming out from the nozzle end, and the rest is a conical shaped plasma arc column with a very bright stream in the middle, and the the sound slightly crackling and buzzing at the same time, and an ever so slight amount of resistance from the wire feed which you may have @ 520 IPM's (Inches Per Minute), then you should be achieving what you want in an Aluminum spray transfer mode... Also, are you pushing the puddle or pulling it??? In other words, are using a forehand technique, or a backhand technique instead and what position are you welding in??? In other words, is it flat, horizontal, vertical or overhead??? Finally, have you gone to the Miller website for some tips on Aluminum welding yet???
http://www.millerwelds.com/resources/articles/Common-MIG-Weld-Defects-GMAW/Don't be dragging your welds when welding Aluminum!!! Push/forehand technique is the only way to go with GMAW Spray transfer with Aluminum unless you want alpine lace swiss cheese within the weld!!! ;) :) :) Also, if you had a different power source like a 350P with pulsing capability, or the newest one's with "Autoset" technology found on the MillerMatic 212 and 252's, you would have to only fine tune your setting as opposed to having the potential of setting too much amperage and voltage and causing much more difficulty in getting the power source to an optimal setting... This is what Larry was referring to with respect to synchronization of the gun and the power source/machine. ;)
Now remember that once the puddle is formed with aluminum, it doesn't take very long for the rest of the base metal to heat up also which means that you'll probably need to increase your travel speed slightly as you moving along the joint, other wise you may encounter the puddle widening on you and excessive reinforcement and/or distortion as well on the base metal, so go with the heat flow when welding 1/2" or less thick Aluminum... Once you get the parameters optimized by tweeking them ever so lsightly towards oyu own personal preferences, you can then ever so slightly adjust the burn back control on the wire feed control. NOT beforehand!!! :) :) :) All the best! ;)
Respectfully,
Henry