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

 

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

 

sprayed some carb cleaner where carb meets manifold - it seemed to steady out a bit - I just got back from purchasing the gasket.

 

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.

 

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.

 

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

 

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.

 

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 !

 

Maybe ran cooler with the shroud on and hotter without it and extra heat loosened up the valve? I know it's a stretch.