I am in the process of tuning the PHBG 19mm carburetor on my AM6 engine after changing the displacement from 50 to 74 cc (Yamaha DT 50 SM, 2007). I purchased three nozzles with calibrations 070, 072, 074 (factory 075), which will allow me to optimize the mixture. With the original settings (nozzle-nozzle) there is great performance, but unfortunately, after a while the plug gets covered with carbon deposits. The engine starts to jerk and loses power. From the cylinder-tube connection, it begins to "spit" oil from under-fired fuel (mixture correct 1:50). After swapping the nozzle from the factory one (075) to nozzle 072, the engine stopped "spitting" oil the candle takes on a brown color (no black deposit). But, as it happens in life, something at the expense of something - the power slightly decreased. However, I am of good thoughts because there are visible effects, I still have other nozzles that will allow me to accurately determine the mixture. So it is worth it to have several nozzles to choose from.
The nozzle fits dellorto 21 carburetors I know because I ordered for such .The product as in the photo and description ie :with a notch for a flat screwdriver and m5 thread.It is useful when we need to adjust the carburetor for example:after changing to a larger cylinder, etc.