5.5 hp brigs and stratton walk behind cycles between dying to ok every 3 seconds

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  #1  
Old 05-13-11, 07:27 PM
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5.5 hp brigs and stratton walk behind cycles between dying to ok every 3 seconds

Here is the dilema:
lawnmower will be on the verge of death then revs up then almost dies then revs up on and on.
I can mow most of the lawn fairly slowly like this without it dying.
When the gas tank is almost empty it actually revs up and runs fine for a minute or two before running out of gas.

Spark plug appears very black after about 1/2 hour of operation.

Description of set up: plastic carb that sits on top of tank.

seems to be similar if not the same as 4.5 HP Brigs and Stratton post
Steps taken: New gas, same condition without Air filter (it was dirty), same condition without gas cap, removed gas tank and carb.
Separated the two, Flushed with water, sprayed carb cleaner, vacuumed and blew dry. there is a metal filter that can fit over a small socket (dog stepped on it..and to reform it) and a long plastic tube with a small screen at the bottom. Blew through both without any real resistance, both appear clean. Multiple cleanings of spark-plug

Only thing I haven't tried is a new diaphragm or new spark plug.

I was thinking it might have been filter related (gas level lowers gunk falls off filter) but on second thought it seems as though I can't figure out why
 
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Old 05-13-11, 07:39 PM
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Follow the instructions on the 4.5 post and you will be good to go, for less than $5. Have a good one. Geo
 
  #3  
Old 05-13-11, 08:02 PM
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any thoughts why it runs so good just before it runs out of gas?
 
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Old 05-13-11, 08:32 PM
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Originally Posted by Flipmstr2 View Post
any thoughts why it runs so good just before it runs out of gas?
As the diaphram ages it looses it's flexability and as such pumps less fuel, when new they flutter and supply fuel in small spirts as they stiffen the spirts become globs as it may take several pulse cycles to activate the diaphram, when the fuel supply is at the end, the diaphram can no longer accumulate enough fuel to create a surge. Have a good one. Geo
 
  #5  
Old 05-14-11, 07:31 AM
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thanks,
I always thought that these small carbs operated much like a garden sprayer where the air flow simply drew the gas in. T didn't realize that that membrane was a pump, just thought it was a gasket/filter combo. (although I was perplexed what the Spring was for )
Gonna get the kit and will advise on the results. Thanks for the help.
 
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