ORIGINAL: ABORH
Thanks for the info. This was the first time I have seen this type of carb, so it would be better to say that it was unique to me. I am not familiar with the engines you mentioned either (and probably quite a few others). I wonder why the piston/sleeve metering is not more common?
You're quite right, it is not common among the engine brands most airplane folks deal with, no nitpicking intended. OPS and Picco are Italian engine makers, in fact the "P" in OPS is for the same Picco, but these are different companies. Rossi is another but
AFAIK they use rotating barrels, I don't own any. Personally I am a bit of an OPS fan so have 5-6 engine with this style of carb. OPS was a very popular brand in AMA pattern in the heyday of the pattern 10cc engines, the gold head "Super 60" is a classic and still a performer by anyone's standards. They are still popular in marine, the .67 and .80 are killer engines. Picco is a significant player in the car engine market and that's one place you'll often see slide valve carbs. For aircraft they require a bellcrank mechanism to give the side to side linear motion while keeping a low frontal profile.
I have no idea if there are functional advantages to one or the other, could be as simple as two different design philosophies.