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briggs/stratton 3.5hp - can't find carb mixture screw

cmkamimura's Avatar
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08-06-05, 03:49 PM   #1  
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!


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dave237's Avatar

Join Date: Oct 2004
Posts: 255

08-06-05, 07:24 PM   #2  


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.

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l.mitchell's Avatar

Join Date: Jul 2003
Posts: 68

08-06-05, 09:08 PM   #3  
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.

Last edited by l.mitchell; 08-06-05 at 09:22 PM.
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