I just got a little 40 kilohertz ultrasonic cleaner, reading up on how to use it. What's a good cleaner formula to use? I've been reading just water with some vinegar and just a drop of detergent works, any other suggestions? Also how long does it normally take to clean up jets with these things? I'm just experimenting with it, at first I didn't think it was working, but now I can see that it is.

Well, I understand some folks use a toilet bowl cleaner… so that’d be an acidic as opposed to caustic…
But different pH values work differently on different metal’s… Perhaps that’s were a little “testing the waters” comes into play…
Sneezles61

Like a little squirt of toilet bowl cleaner into water? I'll experiment with it.

On home brew I would get some aluminum test strips and see what it does. Watch YouTube and see the finish your after and buy that product. I use carb ultrasonic solution 

You can buy proper cleaner in 5 ltr containers of solution and i have found this to doesn't damage anything. It does have some corrosive properties and you do let it down with distilled water @ 5:1 . I find when you take stuff out it's mint. Leave it to cool down and it tarnishes. I just get a soft tooth brush and a rag with some polish on and scrub away for 5 mins. Cleans everything mint.
I experimented with distilled water ,degreaser and spirit vinegar . Mixed opinion about that as it cleaned wiring up a treat as well as steel but crap on aluminium. I got mixed results with baking soda and distilled water too.

For experimental, to start with.. full strength…
I have phosphoric acid that I use for pH adjustment in home brewing beer… never thought to try that and monitor pH solution for cleaning parts…. hhhmmm…
Sneezles61

I saw a video of a guy using simple green, mean green and purple power, and the simple green and mean green seem to work pretty well, when diluted about four to one. The purple power tended to turn aluminum parts dark, so I'm not going to use that. Think I'm going to pull the carburetor and give it a try today with simple green.

They just changed the TSP formula.

TSP - Purple Pine Sol.
45 min. - until hot. 

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I did an experiment with my old petcock, just to see what a gentle degreaser "Super Clean"  would do to aluminum. My little cleaner doesn't have a heater, so I used hot tap water with some of the degreaser mixed in for about 40 minutes. Definitely an improvement, and it didn't harm the aluminum at all.

   
 

Looks like a nice out come!
Sneezles61