18 HP Kohler fuel leak into cylinder and muffler

Discussion in 'Mechanic and Repair' started by hobodewey, Sep 10, 2012.

  1. hobodewey

    hobodewey LawnSite Member
    Messages: 4

    I have an older Gravely Pro-50 (serial # 00629401) mower with a Kohler Magnum 18 HP, Model# MV18S Serial# 2011308286 that I use to mow my personal yard. I went into the garage yesterday and found gas leaking onto the floor. I pulled the float bowl off the carb and found some dirt in it so I removed the needle and float from it, did a little cleaning, and put it back together. The engine would not crank so I removed both spark plugs. One was dry but the other one was full of gas. I cranked the engine over and pumped it dry and put everything back together again. There was gas dripping from a connection on the lower part of the muffler so I did not want to try to start it until it was drained dry so I put a towel under it and let it set overnight. I found a lot of gas had drained onto the floor but no drips coming from the muffler. I pulled the oil dip stick and although it showed low oil, it did not look like it had any gas mixed in it. I started the mower and moved it outside so I could clean the floor when I found what looked like gas/oil mixture pouring out of the crankcase hose vent that exits into the air filter.
    My question is has anyone else ever experienced this before? This engine has a pulse operated fuel pump ( replaced in the last 2 years) and I can't understand how gas can leak past it to the point of filling a whole cylinder. I am going to change the oil and filter and check compression on both cylinders. Any other suggestions??
    Dewey from Michigan
  2. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029


    Fuel is clear and will sit on top of oil and the dipstick is shiny, You think it's possible the fuel was way up the stick and all you seen was the dark oil near the bottom ?

    That's the only way I can think of for fuel/oil mixture to enter the breather system, It's very common for carbs to flood and fill the cylinder. Fuel is so thin it runs right past the ring end gaps into the crankcase, If the exhaust valve isn't fully seated fuel will run into the muffler as well.

    Sounds like your on the right track, Clean carb and change oil..... But....Keep a eye on it because cleaning sometimes doesn't solve the issue, It may take a new float needle valve assembly.....
  3. hobodewey

    hobodewey LawnSite Member
    Messages: 4

    But what I can't understand is how the fuel can siphon past the fuel pump. I wouldn't think that it could gravity feed right through the pump. I disconnected the fuel line and tried to blow through it, but no go. I know I can't blow with much pressure, but it should be more pressure than the gravity flow of gas.
  4. piston slapper

    piston slapper LawnSite Platinum Member
    Messages: 4,337

    Fuel will pass easily thru the fuel pump when the tank is higher than the carb..
    To troubleshoot those units..I frequently bypass the fuelpump if a fuel flow problem is suspect..

    Clean the carb..replace the fuel lines and filter..change the oil..install an inline fuel shutoff...get back to work....
    That engine and mower are old enough to vote...
    Posted via Mobile Device
  5. hobodewey

    hobodewey LawnSite Member
    Messages: 4

    Restrorob and Piston Slapper were correct. The crankcase had more gasoline in it than oil. I changed oil and oil filter, installed a manual fuel shut off where it is highly visible and am back to mowing grass. Thanks guys for your help. And as for the mower being old enough to vote, I think it is almost old enough to retire!
    Thanks again!

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