Carb cleaning - adjustment on 12PT9 chipper
I have a 6 year old 12PT9 MacKissic chipper (B&S Intek 9 HP engine with a Nikki carb) that had been running well until my recent start when it stumbled with choke off. It ran moderately well with just a slight choke. I had assumed that my main jet was probably clogged and I managed to remove the carb. After bowl removal, I found a very clean carb with a newer design that I am not familiar with. It has some molded plastic parts that contain the needle valve and surround the main pipe into the bowl. The pipe appeared to be completely clean. I blew air on the few openings I could approach. I didn't use carb cleaner because it looked so clean and also because I noticed that one of the main gaskets appeared to be slightly offset suggesting an air leak. Admittedly, the offset should have been there for the six good running years. I made my own gasket replacement.
Upon reinstallation without major improvement, I realized that this carburator appears to have no adjustments. Anyone have experience with these Nikki carbs or better ideas on cleaning or adjustment or something else?