Briggs engine coughs and backfires while running with blower housing on

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  #1  
Old 06-12-12, 08:42 AM
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Briggs engine coughs and backfires while running with blower housing on

I am working on a Briggs 31P977-0575-E1 20hp engine on a craftsman rider. The unit came to me with the engine coughing and backfiring through the carb while it was running. I put new sparkplug, new fuel filter, changed oil and filter etc. I also adjusted the valves to .005 and .005 and reset the gap on the coil. The problem I am having is that the minute I put the blower housing back on it starts coughing and backfiring. With the blower housing off it runs perfectly. I have also put shielding on the sparkplug wire and the kill wire. I am now thinking that when the blower housing is installed over the air intake it is somehow opening up a gap between the carb and the manifold or the manifold and the block or there is a crack in the intake manifold. Please help me with your thoughts on how to fix this problem. thanks john lolli
 
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Old 06-12-12, 09:07 AM
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Hello jl66redcpe,

If you suspect a intake or gasket issue, With the engine running at idle spray a little carb & choke cleaner around the gasket areas and intake seams and listen for a idle change.


Good Luck
 
  #3  
Old 06-12-12, 01:23 PM
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sprayed some carb cleaner where carb meets manifold - it seemed to steady out a bit - I just got back from purchasing the gasket.
 
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Old 06-13-12, 08:41 AM
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Installed new carb to manifold gasket. Helped a little but not much -- still coughing and backfire. Just fiinished cleaning carb again just in case. Could not get solenoid off however it seems to be working. More suggestions please.
 
  #5  
Old 06-13-12, 09:49 AM
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Well last thought for the day was a sticking valve. Instead of pulling the head, I added 2oz of sea foam to the oil. Let it run for a while and seemed to be ok. I cut grass to test it and it did not cough under load. The longer it ran, the better it ran. We shall see.
 
  #6  
Old 06-13-12, 05:34 PM
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Well last thought for the day was a sticking valve

Believe it or not that was my thought as well, Sticking or a spec of carbon keeping it from properly seating. But, I couldn't relate that with the blower housing on/off making a difference......


Good Luck
 
  #7  
Old 06-13-12, 05:43 PM
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31yeartech - I am also kind of shocked as well. This engine ran perfect with the blower housing off and terrible with it on. I had also been thinking sticky valve however again, it ran perfect with the blower housing off. This still does not make any sense to me.
 
  #8  
Old 06-13-12, 05:57 PM
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This still does not make any sense

Some things don't, But in this case...... I'm not get'n paid enough to make sense of it.....

Glad it's work'n now !
 
  #9  
Old 06-13-12, 07:35 PM
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Maybe ran cooler with the shroud on and hotter without it and extra heat loosened up the valve? I know it's a stretch.
 
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