Outdoor Power Equipment and Small Engines - briggs/stratton 3.5hp - can't find carb mixture screw

Does my briggs/stratton 3.5hp lawnmower engine have a carb mixture screw? I can't seem to find one. The engine is running really rough and needs to be choked about half way for it to run. Is it possible that I don't have one on this engine? How would one adjust the carb if this is the case. Thx!

Chuck

cmkamimura,

Welcome,

If your mower is a newer model, last couple of years,you most likly will not have adjustment screws on the carb. Throughly, clean your air filter and if this does not help a carb cleaning may be in order.

God Bless,
Dave237

on the older ones adj. is at base of carb. stick screwdriver in sheet metal hole in front by head. eventually you will feel it. if it is a newer one and starts ok but runs rough. replace diaphragm. it is a rubber gasket that sits between carb and gas tank. you will have to take 5 screws that hold carb to tank and lift it out carefully. putting new exactly in same way. they only cost 2-3$ but will make your mower use extra gas and lose power. they get hot and wear. if this is the case it will run like its supposed to immediately. i do not suspect primer bulb because it is starting. i dont think your carb is bowl type but diaphragm type. when pushmower bowl types go bad they wont start. run for a few seconds and stop, or surge{rev up and down). also if you have it off make sure carb is seating to intake pipe. thers is a little ring plastic or rubber that seats them together preventing vaccum leak. diaphragm types also have a plastic screen in tank that could get partially plugged but if i had to bet i would say ck diaphragm.