I'm running a PW50 chinese knock off carb on my 1980 Yamaha Champ. I recently swapped over the mainjet (size 75) from my stock Mikuni over to the PW50 carb. On my recent test ride, it seems to need the choke until it is 100% warmed up. After that it runs and idle off the choke. While riding if I pull the choke up I gain a little speed. This would point me to needing a larger mainjet. What could have changed from different carb models to need a larger mainjet.
I am still running the stock airbox. I did put new uni filter element in it. I would like to get a different pilot jet as well, but not sure what kind of jet it is.