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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 28080
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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I have a Briggs and Stratton model #21b8070296 e1 13.5 I/c

Customer Question

I have a Briggs and Stratton model #21b8070296 e1 13.5 I/c ohv. Murray select lawnmower. The only way I can keep it running is by messing with the throttle. I bring it down until it runs smooth then bring it up to full speed. If I accelerate too fast it will bog out and start backfiring and popping from the exhaust and intake. It seems it it will die under any kind of strain as far as engaging the blades or letting us a break once in gear. I'm kind of lost as what to do. Any idea?
Submitted: 2 years ago.
Category: Small Engine
Expert:  Curtis B. replied 2 years ago.
how old is it? Have the valves ever been adjusted? Have you checked the float bowl in the carburetor for debris or water?
Customer: replied 2 years ago.
Disassembled the carb, it looked practically brand new. Very clean. I checked and blew out everything with carb cleaner. That Didn't change a thing. Also, I checked out the fuel solenoid and it's working properly as well. Not sure of the year or where to find it
Expert:  Curtis B. replied 2 years ago.
Valves ever been adjusted?
Customer: replied 2 years ago.
Not sure how to do that. Let me look it up. I'm just learning as I go.
Expert:  Curtis B. replied 2 years ago.
Look up Briggs intek valve adjustment.
Expert:  Curtis B. replied 2 years ago.
.003 to .005 inch, on intake,, .004 to .006 on exhaust.
Customer: replied 2 years ago.
Okay, looks like I need to pick up some feeler gauges after work tomorrow. I'll let you know the outcome afterwards.
Customer: replied 2 years ago.
If that's not the problem, what would be my next step. Trying to think ahead so that I can pick up what I need while I'm out and about.
Expert:  Curtis B. replied 2 years ago.
Next I would want to check the timing key, between flywheel and crankshaft.
Customer: replied 2 years ago.
What would I check that with?
Customer: replied 2 years ago.
Never mind. I'll look it up
Expert:  Curtis B. replied 2 years ago.
http://outdoorpowerinfo.com/repairs/flywheel_about.asp
Customer: replied 2 years ago.
Didn't change anything.
Expert:  Curtis B. replied 2 years ago.
Valves ok, and flywheel key was ok? Run a compression test.
Customer: replied 2 years ago.
Working on that now. It seems like a compression problem of some sort.
Expert:  Curtis B. replied 2 years ago.
OK>
Customer: replied 2 years ago.
Can't find a compression tester. It fires up right away. Do you think it could be a compression problem with that being the case? Also, I replaced the spark plug yesterday and it is solid black today. Not sure if that means anything.
Expert:  Curtis B. replied 2 years ago.
Black means too much fuel , not enough air! Is the choke flap fully open?
Customer: replied 2 years ago.
I have black smoke, choke is fully opened. I can get it running wide open, sounding good, and no smoke but, as soon as I engage the blades or put it in gear, it dies.
Customer: replied 2 years ago.
I have to idle down until it starts running smooth and smoke stops then slowly being up the acceleration.
Customer: replied 2 years ago.
Could it be a bad muffler?
Expert:  Curtis B. replied 2 years ago.
Sounds like timing to me! But easy enough to slip the exhaust off and test.
Customer: replied 2 years ago.
Or could it be that the manifold is full of trash
Expert:  Curtis B. replied 2 years ago.
With out any history, you never know!
Customer: replied 2 years ago.
Yeah, I hear ya. I'm getting the same thing just louder. Lol!
Expert:  Curtis B. replied 2 years ago.
Did the flywheel key show any damage?
Customer: replied 2 years ago.
No, I figured it out though. When I cleaned out the carburetor, I Failed to put the jet back in place. Thank you for your time
Expert:  Curtis B. replied 2 years ago.
Good job, lesson learned! Thanks,