I had a few stationary engine carbs like that and found a bit of washing up liquid and a sonic cleaning bath, mine was £30 or so at Lidl, so not anything fancy or expensive was enough with a toothbrush to scrub afterwards had the carb sufficiently cleaned to do its job. I had the sonic cleaning bat running for a whole afternoon mind, just for 1 carb, you have 4. Probably worth getting someone with better sonic cleaning baths than the cheap ones.