Flooded B&S engine

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  #1  
Old 07-02-08, 03:34 PM
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Flooded B&S engine

My grandfather called up and told me he was having new troubles with his lawnmower. He had completed about 2/3 of the lawn when it backfired and quit. It proceeded to start right back up, and he finished mowing. Just as he was putting it away, it backfired and quit again. He put it away and did not attempt to find out what was wrong.

I went to look at it the next day, and discovered that it now would not even turn over. It was partially siezed, in that I could turn it by hand a few turns, and then it would stop. He had previously bought a new head gasket set, because he overfilled the oil last year, which caused a set of problems that seemed to cure themselves, until now. So I decided to change the head gasket.

When I started to empty the oil out of the sump, it became evident that gas had mixed with the oil, to the point that the liquid that came out of the sump had a viscosity much closer to gas than oil, and in a quantity that was much larger than the sump capacity.

While changing the head gasket, I had a "duh" moment and realized that the gas in the oil probably would not be caused by a blown head gasket, and it must be the carb. However, the old head gasket had defects in the area between the two chambers. It's hard to tell if if was actually blown or not.

I got the engine put back together and got it started back up and running just fine. I ran it for about 15 minutes, and didn't notice any gas in the oil. But to be safe, I turned the valve on the fuel line off until I figure out what is going on.

Here is the info on the engine:

15 HP OHV
Model: 28N707
Type: 0635 A1
Code: 9510264A


According to the parts list, the carb is a Walbro and the part number is one of the following: 698620, 693773, 698782. I haven't had a chance to verify which it is.

I'm wondering what might be causing the fuel to leak into the engine, when the engine runs just fine. Since the oil was well mixed with the oil, it must have been leaking while the engine was running, no?

The carb has a fuel servo on the bottom of the bowl, might that have failed? I'm just grasping at straws right now. Any ideas would be greatly appreciated.
 
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  #2  
Old 07-02-08, 05:45 PM
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Location: Lake charles
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The gas likely leaked into the crankcase while the engine was not running. This is caused by a faulty needle or seat attached to the float. As long as the engine is running it will burn the gas faster than it is leaking.
Always check the oil level before using. I had a B&S a few years ago that this happened to. I checked my oil & found it over the fill mark. It smelled like gas. The needle valve was not cutting off the flow to the carb. When the bowl ran over it flowed back into crankcase via the intake & cylinder.
I installed a manual cutoff between the tank & carb.


Regards,
John 3:16
 
  #3  
Old 07-02-08, 07:47 PM
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Most likely it's leaking at the inlet needle on the float. The fuel solenoid will not and I repeat will not keep an engine from flooding, no matter what! If the engine runs then the solenoid is good.

If you shut the fuel off when your not going to use it for awhile, it will prevent this from ever happing again.

698620 shows to be the carburetor for your engine if it's a Walbro. You probably only need to replace the needle 231855S, but if you put a new one in and it continues, then you may also need to replace the seat.
 
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Old 07-03-08, 11:50 AM
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Thanks for the replies. He cut the yard today and didn't have any problems, so hopefully replacing the head gasket solved the backfire/quitting problem. I'm going replace the inlet needle and seat in the carb since I know it's only a matter of time before he forgets to manually turn off the gas. Thanks again.
 
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