QuestionGood to know you're back taking questions. I have a B&S 3.75 Sprint lawnmower engine and all of a sudden it is running rough. There seems to be a lot of carbon on a new plug I just installed. So, I "think" it needs some carburetor adjustment but I can find no adjustment screw. When I push forward a little white, plastic boomer-rang shape object to the side of the intake of the carb, it seems to run smoother and a little more fast. The engine ran just fine last week, so I also put in fresh gas with a little bit of fuel additive to clean the carb (which is as clean as day one). It runs rough whether the foam air cleaner (newly cleaned) is in place or not, if that helps you.
Many thanks and I look forward to your wisdom.
Bill
AnswerThe carb is not adjustable. When the engine starts to run rough, the most likely problem is the carb. Most likely you will have to remove, dis-assemble and clean the carb with compressed air from an air compressor.
You may want to purchase a diaphragm kit before you tear into the carb. Pay attention to how the diaphragm and gasket are arranged; the old diaphragm and gasket will appear to be one part...just pay close attention.
The carb is very simple. Just use about 40-60 psi of air pressure to clean the carb and tank.
Let me know what you find.
Eric
