Help troubleshooting craftsman mower with 21 hp motor

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Old 03-29-15, 12:04 PM
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Help troubleshooting craftsman mower with 21 hp motor

Hey folks, last time I mowed the motor noise changed to a deeper sound and eventually started missing. Checked the sparkplug but looked okay not wet with fuel. Sounds like it is getting too much fuel. Moved the throttle lever up to choke and that is the only time I see anything move on the carburetor, is that normal? I Engine is a Briggs and Stratton.
 

Last edited by Tbuc79; 03-29-15 at 02:35 PM.
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Old 03-29-15, 03:32 PM
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The sparkplug was a chocolate brown on the end of the electrode or was it blackened? If it was getting too much fuel (enough to cause the miss) it should be black and sooty.
 
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Old 03-29-15, 04:03 PM
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What you described on the carburetor is normal. What engine do you have? It may be a valve issue if it's the engine I think it might be.
 
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Old 03-29-15, 08:41 PM
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It is more black and sooty
 
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Old 03-29-15, 09:24 PM
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21 hp Briggs and Stratton model# 917.28722
 
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Old 03-30-15, 12:42 AM
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The model of the engine is what we need. Is it a single cylinder?
 
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Old 03-30-15, 03:49 PM
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Yes it is a single cylinder
 
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Old 03-30-15, 07:28 PM
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Check to be sure the choke is releasing on the carburetor. If not, move it manually and it should run better. Cleaning or replacing the choke shaft in the carb would fix that.

If it's not the choke, check the valve clearances. See how wide they are and report back before trying to adjust them.
 
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Old 04-06-15, 08:37 PM
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Problem Solved

Just wanted to give everyone an update on my 21 hp Briggs and Stratton engine model# 331877. My engine started running rough and I noticed it was exhausting through the air filter so thought maybe the valve was stuck. I took the valve cover off and found the exhaust valve rocker arm had loosened up because the stud holding the rocker arm had vibrated loose. Secured the stud, installed the rocker arm, reset the clearance and I'm back in business. Thanks for the help and ideas.
 

Last edited by Tbuc79; 04-06-15 at 10:12 PM.
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