Craftsman 25 hp lawn tractor runs rich

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  #1  
Old 07-24-04, 04:04 PM
henry
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Craftsman 25 hp lawn tractor runs rich

During a long day of mowing, my craftsman 26 hp 46" deck lawn tractor started running very rich, lots of black smoke, low power, etc. In fact, really not enough power to mow. It is as if the choke were engaged. I checked the choke cable position and it seems to be correct.

This only happens under load--when it is running with the blades off or even with the blades engaged in an area where there is no grass it will rev freely and doesn't smoke at all.

The air filter has been cleaned, I can't find any way to adjust the mixture, even tho the owners manual says that it can be adjusted. It is a model 917.272201.

Does anyone have any ideas?
 
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  #2  
Old 07-25-04, 02:14 AM
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Hello Henry!

Sounds like a clogged air filter. I know you said you cleaned it, but it can appear to be clean and still be clogged if the pores in the paper element are filled. A wet filter will also do this. Also, check to be sure the oil doesn't smell like gas. Make sure the choke is opening completely too.
 
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Old 07-26-04, 06:17 PM
henry
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I replaced the paper filter and cleaned & oiled the foam filter per the manual. No difference.
When the blade is not engaged, the motor runs fine. On any setting above 1/4 throttle with the blade engaged (not mowing, not moving the tractor, just spinning the blade) black smoke comes out of the exhaust and the engine runs really rough. When it is doing this, simply disengaging the blade return the motor to normal. Without the blades engaged the motor revs freely and just seems totatlly fine.
I tried cleaning the blade housing just on a wild notion, but that didn't make any difference.
Sears charges $185 just to come out and look at it.
Does anyone have any other ideas? Could a clogged muffler do something like this?
 
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Old 07-26-04, 10:49 PM
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Doesn't sound like a muffler problem. It's an odd problem. Have you checked the cooling fins to see if they are clogged with debris? A long day of mowing with clogged fins would have been enough to overheat the engine. Does it do it when cold?
 
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Old 07-27-04, 04:53 PM
henry
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It does it whether hot or cold.

If it were a car I would think that the fuel pressure regulator was bad, allowing fuel to be forced past the jets. But I doubt that a lawn tractor even has a fuel pump.

I blew all the debris off the motor (after taking the covers off) but that also didn't make any difference.

Some older Briggs engines had a mechasim to compensate for load by adjusting the mixture. I don't see any such device on this motor, but I may not be looking in the right place for it.
 
  #6  
Old 07-27-04, 05:53 PM
henry
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One more thing...I did smell the oil and it has lots of gas in it...

The filters, the oil, etc. everything in the routine maintance category was done at the start of the season. Also two of the three blade mandrels were replaced, since the old one were leaking ball bearings. The underside of the deck was pressure-washed at the time and the belts were all checked.
 
  #7  
Old 07-28-04, 12:01 AM
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Ahhh...now we know. The fuel in the oil tells all. You have one of two problems. Either the carburetor needle is not sealing off the fuel, and it is flooding the engine, or, the fuel pump has a bad diaphragm and is allowing fuel to enter the engine through the crankcase pulse line.
 
  #8  
Old 08-07-04, 07:52 PM
henry
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Problem solved

I went to the Sears repair facility and talked to one of their techs. He said that replacing the carb was the recommed solution. Sears techs say that the carb can't be reliably field-rebuilt.
I went to the parts counter and ordered the carb--the parts list said that this carb had "limited availabilty" and that the parts stores should not order these for stock.
Replacing the carb fixed the problem. Although I thought that it happened suddenly, there is now so much more HP that there must have been a gradual deterioration; fuel economy is also now much better.
But, I don't understand what would have happened to cause the carb to flow more fuel. My usual experience has been that the fuel flow is cut off by gum build up, etc.
 
  #9  
Old 08-07-04, 08:06 PM
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float had pinhole leak in it or needle and seat were not working because of dirt or wear.
 
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