Brigss & Stratton won't run with air filter

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  #1  
Old 06-04-07, 10:59 AM
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Brigss & Stratton won't run with air filter

Hello. I have a Craftsman lawnmower with a Briggs & Stratton 6 HP engine. The lawnmower model is 917.388720 and the engine model is 12H802-2639-B1. The engine has been surging intermittently so I pulled the carburetor, removed the gasket, float and needle valve then submerged it in a can of GUNK carburetor cleaner for 20 minutes as instructed on the can. Then I washed it, blew it out with compressed air and reinstalled it. The engine will run with the air filter off but it will not run with it installed.

It still surges somewhat. If I open the throttle it does not surge; it runs fine. (It's a fixed throttle but can be opened manually).

I noticed that there is a small horizontal hole through the threads on the nut that holds the fuel bowl on the carburetor. The hole is clean and not obstructed. Is this hole for fuel metering?

Does the nut need adjusting or not?

Why won't the engine run with the air filter installed? (It's a new filter).

I'm guessing there is still something restricting the fuel flow. Should I soak the carburetor longer, maybe 24 hours?

Could the surging be caused by something else? Maybe something wrong with the governor?

Thanks.
 
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  #2  
Old 06-04-07, 12:06 PM
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I'd say that the carburetor is fine. Although the air filter is new, I'll bet that it is clogged with gasoline. It may not look dirty but it must be clogged.
 
  #3  
Old 06-04-07, 01:56 PM
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Thanks Puey. I'll try another new filter and see if that helps.

Why would the engine still surge a bit even with the filter off?
 
  #4  
Old 06-04-07, 05:41 PM
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The bowl nut is the main jet and this is not adjustable nor are there any adjustments related to the fuel delivery. The Gunk product you used, was this a spray can of cleaner or a bath type cleaner? In either case, and this is only my opinion, I don't care for Gunk products. I have had no luck with them when I have been forced to seek alternatives when my normal cleaners (Napa # 6402, bath cleaner, and, Briggs & Stratton #100042, spray cleaner) are on backorder from my supplier. I'm sorry, I thought the surge disappeared and since any surge will be related to a lean condition, I recommend using both of my suggested cleaners, at least start with the spray cleaner. And if this is not enough then the carb should be soaked in the bath cleaner for 15-20 minutes and then spray it off immediately with the spray cleaner and then install a Briggs rebuild kit, part number 498260. If you suspect that the main jet (bowl nut) is not cleaning well then I suggest replacing it with Briggs part number 494870.
 
  #5  
Old 06-05-07, 11:39 AM
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The Gunk product I used is the bath type. I've used it before with very good results.

I will try the other cleaners and parts you recommend.

Does the bowl nut have a vertical as well as horizontal metering hole in it? I'm thinking it must in order for the fuel to be drawn up into the carburetor.

Thanks very much.
 
  #6  
Old 06-05-07, 08:29 PM
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Yes, the nut has a vertical hole as well.
 
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