Gas in crankcase

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  #1  
Old 09-12-07, 01:57 PM
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Unhappy Gas in crankcase

I have owned 3 B&S L-head mower engines dating 1989, 1993, 2003. 8, 8, 9 hp respectivly. No problems from the 8 or 9hp engines. But the 8 (1993) , M/N-196702, Type-0142, has a recurring problem. I bought this mower (Troybilt) used in April 2007. It ran fine for a month. I filled the gas tank and started to mow a lawn. It ran out before I could finish. I didn't understand why. I poured some more gas in the tank and realized it was running out of the cracked breather hose. I thought "stuck float". I replaced the float and pin, needle, seat, gasket and breather hose. I ran it fine until last week and it did it again last week. I realized that gas was getting into the crank case. This time, I replaced the float and pin and the breather hose. I flushed the crankcase with fresh oil and filled it again. It started fine, ran fine, but I didn't cut anything. Because of rain, it sat for 2 days. All of the gas drained out of the tank and into the crankcase. What is causing the problem? Neither the 1st nor the 2nd float had gas in them. A needle and seat shouldn't go out in 3+ months. I have never had to repair a small engine carb before because, I have had them last 27 years. I will rebuild the carb, but I just wonder, what is the real problem? Your experience and input would be welcomed.
 
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  #2  
Old 09-12-07, 04:34 PM
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You said you replaced the inlet seat, are you sure you did? This is a pressed in seat and isn't something the average homeowner can do without knowledge of having done so before. Regardless, the first thing that comes to mind is that you may have a miniscule scratch in the bore of the seat. Just another thought, by any chance have you installed an aftermarket electric fuel pump on this engine?
 
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Old 09-12-07, 07:56 PM
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Removing and installing the seat is a simple process. The rate of flow is greater than a scratch could cause. If I rebuild the carb, I will again change the seat. The carb is still gravity fed.
 
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Old 09-12-07, 10:39 PM
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If you have the pressed in brass eat Puey61 mentions, it's not a simple process. Since you said it is, I assume you must have the rubber seat? If so, did you install it right side up? Is there a dent in the side of the bowl?
 
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Old 09-13-07, 04:11 AM
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I have 30+ years of tool and die, machine repair and auto repair experience. Changing the seat was not a problem. I could just buy a new carb, but I would like to solve this problem and not spend $135. I installed the solid seat, the needle has the soft tip. I was told this was the best combination. They also offer a soft seat with a solid needle. The bowl has a bump out on the lower side. I have been lining this up with hinge pin side of the float.
 
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Old 09-13-07, 11:55 AM
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Cheese was asking about a dent, not a bump. He was alluding to the fact that if there was a dent in the bowl that it could interfere with the proper operation of the float and thereby cause a fuel leak since the inlet needle may not seat well. When you had the carb upside-down and installed the float, do you recall the position of the float relative the the carb body? The float should be at or near parallel with the body. Anything other than such I suppose could cause a leakage past the inlet needle tip. What I'm thinking is the possibility of the seat not being fully inserted into the carb body which would have an effect on the proper operation of the seat and needle. Just so we know, if for nothing else other than the year of the engine, what is the code number of the engine. This will tell us how old it is.
 
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Old 09-13-07, 04:39 PM
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There is no damage to the bowl. I removed the carb back in May, but not this week. I spent an hour on the phone today w/ B&S. The tech and the service shop where I buy parts agree that a carb rebuild is not neccessary to deal with this problem. The seat, needle and float are the components that control the gas. They don't understand why the 1st fix only lasted 4 months. I am going to pull the carb again and replace the seat and the needle again. I have some apprehension about pulling that seat too many times. The aluminum casting has its limits.

The engine is a late 93'. The code is - 9312181A. The seat p/n is 690577. The needle p/n is - 231855S. These are the parts for the later version of this engine. The float is - 494381. The carb is a LMT.
 
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Old 09-13-07, 07:26 PM
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Ok...now I see. To you, changing the seat was a simple process. To the average homeowner, it is not.

I agree with your apprehensions. The seat generally does not wear or just "go bad". Usually a leakage problem is due to the needle, a bad float, sticking hinge pin area, or dent in bowl. I also had this same problem with several of those carbs for a short while. It turned out to be a bad batch of needles best I can tell. They were black-tipped needles...and nearly every one I used leaked. I went through all the frustrating head sctratching you're going through and then some. I finally figured out that the ones with the black tips leaked. Maybe you've got a bad needle? Is it original Briggs equipment?

If the rate of flow is greater than that which would be caused by a scratch, then I don't see how the seat could be to blame. Sounds like something else.

If it were just a scratch, I have used rubbing compound on the tip of a q-tip, driven by a drill, and inserted into the seat to buff out irregularities with success.
 
  #9  
Old 09-13-07, 10:31 PM
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The needles have a gray tip. I will go out to the garage tomorrow to see if they are genuine B&S parts. I received a private email, suggesting the possibility of a blocked bowl vent contributing to my problem. I am going to see if and how the bowl is vented and if it is blocked.

The mechanics of repair are routine for me, based on my experience. But the ability to troubleshoot and analyze is the step beyond turning the wrench. I would take a small engine repair course, if I could find one in my area. I have 3 mowers, a tiller, 3 trimmers, 2 blowers, 2 snow blowers, a pressure washer and 2 generators. I need to buy a chain saw, a trash pump, a smaller generator and another mower. My son and daughter expect me to repair their equipment and my daughter also has 2 motor scooters and they are looking for 2 jet skies. I could use the formal knowledge.
 
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