Backfire through the carburetor.

J

Jdeere123

Forum Newbie
My John Deere lawn more just started backfiring through the carburetor. It’s a 20004 L 1 20. What would the possible causes for the backfiring be. I have change the plugs air filter fuel filter and oil.
 
What engine do you have on your mower ???? I'm betting on a Briggs twin cylinder...........

Model number from the engine is a must for us to help you out further.............

Let us know Mon Ami ~!~!
 
Boudreaux In Eunice La. said:
What engine do you have on your mower ???? I'm betting on a Briggs twin cylinder...........

Model number from the engine is a must for us to help you out further.............

Let us know Mon Ami ~!~!
Click to expand...

Right you are! The model is a 406777 type 0139, E1 code 040203YG. This number came from the valve cover.
It is in a John Deere L120.
Thanks
 
bertsmobile1 said:
A bad cam, loose valve seat, bent pushrod , broken timing key , lean carb.
Click to expand...

That is a pretty good list. I will start with the lean carb just because I am an optimistic sort. The valve train will be my next effort. I noticed that you did not include weak coils or spark. I believe other items all involve the engine to be removed and disassembled.
Thanks for your suggestions. I will let you know what I find.
 
After the carb, start with the valves....... Pop the valve covers off and check your rods for a bent one, then while turning the engine over look at the rockers to see if the travel is the same........

Adjust the valves to 4 thou and 4 thou....
 
Boudreaux In Eunice La. said:
After the carb, start with the valves....... Pop the valve covers off and check your rods for a bent one, then while turning the engine over look at the rockers to see if the travel is the same........

Adjust the valves to 4 thou and 4 thou....
Click to expand...

I could not find adjusting screws for the carburetor. I know some are not adjustable.
I went through and adjusted the valves to .004 and rechecked them.
I checked the spark and it looked blue and bright.
Started the engine and it still pops through the carburetor worse under load.

Do you know what the lift should be on the valves? The clearance to start with was from.015 to .030 so I would think the cam was good

I am doing a compression test next to see if I have a valve problem.
It will run with the left plug disconnected and will not start with the right plug disconnected.

Thanks again
 
I just experienced this with a ~14HP Briggs & Stratton engine. Every fourth or fifth compression stroke a loud bang and fire from the carburetor would occur. Decided to part out the engine and entire mower due to a list of other issues. However, during disassembly, I came across a completely sheared flywheel key (cut in two pieces) once removing the flywheel.
 
Some of those engines run a diode between the two coils to prevent phantom sparks.
So try the engine again with the kill wires removed from the coils
Running the mower for a few minutes wit the cover off while you are diagnosing the engine will not hurt it but don't go mowing with like that.
he carb solenoid should stop the engine but you might like to keep some insulated pliers handy to pull the spark lead or make up a pair of jumpers to ground the coils.
 
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