It could be that the idle gap is too large. Close it until the engine idles lower, until it almost shuts off. Then run it around, and listen for the idle. If it is good, then idles high the engine is most likely lean on bottom. If it comes in good, and the idle drops its probably too rich on bottom. If the idle stays steady on the bottom it is close. When the idle stays steady, then adjust the idle gap until it is where you want it. It will take some fine tuning from there.
The low speed needle should be just outside of flush with the housing on the Roma.
Both of those engines should drop to a low steady idle.
Feel free to call for more details on tuning.
