Update on riding mower engine going chugga chugga.

Discussion in 'Shop Talk' started by mary,tx, Sep 18, 2004.

  1. mary,tx

    mary,tx Well-Known Member Supporter

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    After downloading parts drawings at B&S web site and a few trips to town for parts, I still have problems with my riding mower engine. We do not have a tractor yet and so this is the only chance I have at keeping the weeds at bay and they need taming badly. (I have a pull behind Rough Cut Trail Mower purchased at the Tractor Supply and it runs great. It has its own engine to run the cutting blade. I just need something to pull the mower.)

    I have a 2Cyl B&S riding mower engine that is running rough. Smoke is black and sooty. Looking down through the carb with the air filter removed, I could see some liquid fuel at the bottom where the intake manifold bolts on and makes a 'T'. It also appeared that there was fuel around the base of the air filter as if too much fuel were being sprayed about. (I did not dare try to run the engine with the air filter off.) There is only one adjustment (Idle mixture) and it does not seem to do anything in this situation.

    When I disconnect the fuel line and start the engine it still runs rough, but at the last instant the engine runs great for a second or two. Hooking the fuel line back up, and restarting the engine runs great for a short while apparently until the carb fills up with full and it runs rough again. The gas is only a couple of weeks old.

    I cleaned the air filter, put on new fuel filter, new plugs, and put in a new carb/fuel pump kit. I could not get the needle valve seat out so it is original--it has nothing to grab onto or turn to pull it out. (any ideas?) I saw no grit in the carb when I pulled it apart and just a little fine sediment in bottom of the fuel resevoir. After putting the carb back together I got the same results--it ran great for a short while, then it went back to chugga chugga chuffa.

    This tells me that the engine is cabable of running well (and the gas is not the problem). I don't think it is the needle valve since with the fuel line disconnected it still runs rough for awhile until the fuel is almost depleated from the resevoir.

    Any ideas what would make it burn so rich?

    Notes: B&S Model 42A606 Type 12380-01 Made in 1997. The fuel pump is the small rectangular kind on the front of the carb. The fuel resevoir is inside the carb and the intake manafold bolts on the bottom of the carb, then splits to the two cylinders.

    By the way, thanks for the previous comments, but I need something else to try.

    Thanks,
    Dale (dh of mary,tx)
     
  2. moopups

    moopups In Remembrance

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    The description of the problem leads me to think it is one of two things. 1 The float is not working correctly, take off the carb, place a piece of hose on the inlet port where fuel comes in. Withthe float bowl chamber bottom off of the unit, the float will hang down, now blow air (with your mouth) into the hose, slowley push up the float gently until it is horizonal, at this time the air should not flow into the unit, if it does bend the little tab that contacts the neddle valve until it stops air flow when horizonal. If that works correctly;
    2. The float bowl vent is clogged. Air in the bowl must escape when fuel enters it, this is done by a tiny hole to the outside air. If this vent is clogged the fuel will compress the air inside of the chamber which in turn will put that pressure on to the fuel. The fuel will not compress but will react to the pressure - react by flowing through the main jet opening up into the carbs venturi where it floods the cylinders with too much fuel. The hole is tiny, less than a pencil lead diameter. This is the classic cause and effect for the problem you are experincing. There needs to be visual proof that the vent is open such as spraying wd 40 or similiar the see positively that it is open. The hole is located in the top part of the carb, usually near the middle of its mass, its size is about the same as the wire used in a small paper clip. I mentioned this in the earlier post but you did not comment on it so I must think it was overlooked, I have seen this problem stump many mechanics in the past.
     

  3. agmantoo

    agmantoo agmantoo Supporter

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    If the needle and seat is not functioning ( which I think is the problem) and the fuel tank is located higher than the carburetor, the carburetor should leak fuel after the tractor sets for some duration. The gas leak is the indicator of the poor seating. This is why the tractor runs properly when you disconnect the fuel. Under the disconnected situation at the last instant the amount of fuel available to the carb is correct and the flooding ceases and the engine runs as it should.
     
  4. mary,tx

    mary,tx Well-Known Member Supporter

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    Thanks for the tips guys, I will check these things out this comming week though I have Jury Duty and don't know my schedule.

    The fuel tank is below the carb (actually it is tall enough so when full, fuel is higher, but only 1/2 tank at the moment.)

    The vent appeared clear when I was cleaning it, but I will take special care to make sure, especially that a gasket does not block the hole since there is some play though I think I remember the hole showing when I put the air cleaner back on.

    The thing the confuses me is that when I take the gas line off and there is no fuel entering (except for the very small amount in the pump), it still runs rough until the last moment. With no fuel coming in and what is being burned comes from the resevoir, I really wonder if it is the needle valve.
    Thanks,
    Dale (dh of mary,tx)
     
  5. moopups

    moopups In Remembrance

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    When it runs rough at the last with the fuel line off is because there is still too much fuel in the float bowl,the running right is when the level gets to normal for a brief period of time. Also look at the pointed cone end of the neddle, is there a tear in the rubber? This applies to the rubber tiped ones. Is there a scored mark on the end of the solid metal tip? Either means mechinical failure and a need to replace either.
     
  6. mary,tx

    mary,tx Well-Known Member Supporter

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    Moopups,
    I put in a new needle valve, but I could not get the seat out. There was nothing to grab to pull it out. I am going to try to bend the tab on the float a bit to see if that helps.
    Thanks,
    Dale