Sounds like a good first try, but I totally get your underwhelming reaction. I’ve had similar experiences when I first used an ultrasonic cleaner for engine parts. The key for me was getting the right balance of cleaning solution and temperature. I started using ultrasonic cleaning tanks and found that measuring the powder properly made a big difference. Also, I found that running longer cycles with the temp a bit higher, around 60°C, worked better for stubborn carbon buildup. Patience is key, and I also found https://www.kaijo-shibuya.com/industrial-ultrasonic-cleaners/ultrasonic-cleaning-systems/ pre-soaking the parts in a stronger solution overnight helped.
Heat is definitely key in this. I have been experimenting with few different solvents, one degreasing wash worked great but sadly I'm all out of that. Citric acid works good in there for rust. Haven't found any solution to be far above others though.
1st try of Ultrasonic Cleaner.
I thought I had an old 376 carb, but couldn't find it so stuck my 3 old pistons and 6 old valves into this cleaner. I had bought some UltroCarb powdered cleaning medium that should be disolved at 20g per litre of water. I wasn't too fastidious in measuring this.
I set the machine at 50* and ran 3 x 5 min cycles.
Not sure how good it is for removing years of burnt on carbon
I have to say I am underwhelmed, although I believe it is operator error maybe not enough powder and/or temp not high enough.
Conclusion; jury is out on my first attempt. I'll need to find something else to try and accurately measure the powder required.
Anyone with experience of u/s cleaners please feel free to chip in with any advice/info/hints/tips.