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Riding mower backfires while trying to start but won't start up


Nubaesa's Avatar
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07-23-16, 02:14 PM   #1  
Riding mower backfires while trying to start but won't start up

I have a Poulan 38" cut riding mower. B&S 15.5 hp engine, model# 282H07, type#: 0231E1, code# 031222ZE. The mower was purchased new in 2004. Until recently it was starting and running fine.

So far I've changed the spark plug, air filter, cleaned the carburetor, cleaned the magneto and flywheel contacts, pulled the flywheel and checked that the key is intact and adjusted the valves.

Does anyone have any ideas of what else to check?

 
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07-23-16, 02:50 PM   #2  
Is fuel running freely from the Tank to the Carburetor; no clogged Filter, or Fuel Solenoid ?

 
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07-23-16, 03:03 PM   #3  
Sounds to me like you need to adjust the valves. Have a good one. Geo

 
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07-23-16, 03:33 PM   #4  
Already adjusted the valves and fuel is flowing freely to carb. Check fuel solenoid and it's working fine. Thanks for trying to help. Have a good one.


Last edited by Nubaesa; 07-23-16 at 03:50 PM.
 
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07-23-16, 04:21 PM   #5  
Is it backfiring back through the carb or out the exhaust. Have a good one. Geo

 
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07-23-16, 04:55 PM   #6  
The popping seem to be coming from the exhaust. The other day when it backfired, I had the air filter off and a small flame shot up through the intake side of the carb.

 
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07-23-16, 08:23 PM   #7  
Was it doing this prior to the valve adjustment and the removal of the flywheel? Because it sounds like either the valves are adjusted improperly or the flywheel key has sheared. Did you put oil or grease onthe shaft where the flywheel fits? What was the valve adjustment procedure?


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07-24-16, 09:43 AM   #8  
It wasn't doing this prior to valve adjustment. I rechecked the valve clearance (.003 - .005 intake and .005 -.007 exhaust). The notch on the shaft and flywheel are aligned with the key. I did not put oil on the shaft. The valves were checked while the piston was at tdc and neither valve was moving.

 
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07-24-16, 10:08 AM   #9  
Last time I checked prior means before. So everything was great till you adjusted valves?

 
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07-24-16, 12:22 PM   #10  
The reason I adjusted the valves the first time was because when I tried to start it, it would spin or attempt to spin and seem to bogg down. I looked at a few videos that indicated the valves need adjustment because of too much combustion in the chamber to allow it to spin freely. When I adjusted the valves, it started spinning as usual and started right up. Cut my grass and put it away. Tried to use it a couple weeks ago and that's when the backfiring started.

Last night I loosened the valves and adjusted again. The backfiring stopped but it still wouldn't start. Tried a couple squirts of starting fluid but still nothing.

I looked at a couple of videos this morning for adjusting the valves on the B&S 15.5 I/C engine. Both videos indicated that the intake valve is the top valve. Looking at my engine, the top valve is near the exhaust port. When I first adjusted the valves I adjusted the top valve to the exhaust settings. Since I didn't have much to loose, I readjusted the valves according to the video (top valve being the intake). Well it's back to backfiring again. Before I change it back, do you know which is intake and exhaust.

 
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07-24-16, 12:55 PM   #11  
The engine needs to be 1/4 inch past TDC when you adjust the valves, remove the spark plug insert a thin screwdriver to measure the 1/4 inch. Have a good one. Geo

 
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07-24-16, 02:29 PM   #12  
Thanks Geo, I stumbled upon the 1/4" past tdc this morning. I'll try that when I go at it again. Can you tell me which valve is intake/exhaust? Looking at my engine, the top valve is near the exhaust port connected to the muffler. The how to videos tell me the exhaust valve is the bottom valve. I'm so confused.

 
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07-24-16, 02:46 PM   #13  
It doesn't matter which is which, set them both to .005" and you'll be fine. It doesn't sound like you are setting them correctly.


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07-24-16, 02:55 PM   #14  
Top is intake. Set both to .005 after rotating flywheel to 1/4 inch past top dead center on compression stroke. After you set them spin the engine over a couple of times and check both lashes at TDC - the exhaust should have no lash at that point and the intake should have .005. Then rotate the flywheel to move the piston another 1/4 inch down in the cylinder. At that point both clearances should be .005.

If you have that, the compression release is working and you're ready to mow.

 
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03-22-18, 02:12 PM   #15  
Backfiring after it starts

just changed my fuel lines on a 18.5 b&s has a fuel pump on it they were pretty rough! Before I changed them mower operated fine! Now it is backfire right after it starts can someone tell me what the problem may be?

 
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03-22-18, 05:50 PM   #16  
Not really sure what could have changed...could be unrelated. Did you also change the vacuum line to the fuel pump?
Does it backfire once or continue?
What is it on, and what model...Intek? On a riding mower?


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03-22-18, 07:49 PM   #17  
Usually a fuel problem right after changing lines is caused by bits of brittle crumbling rubber that got broken off the lines and into the carburetor.


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