# Briggs engine coughs and backfires while running with blower housing on



## John Lolli (Nov 3, 2005)

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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## geogrubb (Jul 28, 2006)

John Lolli said:


> 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


While it is running spray some brake/carb cleaner behind the carb and along the intake mating surfaces, if the engine tempo changes you have found a leak. Have a good one. Geo


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## John Lolli (Nov 3, 2005)

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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## John Lolli (Nov 3, 2005)

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.


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## John Lolli (Nov 3, 2005)

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.


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## usmcgrunt (Sep 16, 2007)

Have you tried putting spark testers on both plug wires and observe which cylinder may be cutting out when the housing is installed? If you can isolate the problem to one cylinder,you may find a coil cutting out due to a short or poor ground to the coil.Don't know,just guessing!

Glad you got it working,we were posting at the same time.Good job


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## John Lolli (Nov 3, 2005)

USMCGrunt - thanks for the response. It is a single cylinder engine. I know, it is strange that a 20hp briggs is single cyliner however it is.


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