AboutEric A. Jones Expertise Lawnmower Repair . Certified Master Service Technician from B&S. Have 13 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.
Experience Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. I received a scholarship from the Air Force and am currently pursuing another degree.
Question Good 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
Answer The 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.
