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Thread: Kohler vee-twin 20hp petrol.

  1. #1
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    Kohler vee-twin 20hp petrol.

    Just a long shot. I have a ride on mower with a 20hp vee-twin petrol Kohler.

    Yesterday I started it and was just about to put the deck into gear and she suddenly stopped. She wouldn't start so back in the workshop. Took both plugs out and put one back in the HT lead and earthed it and cranked the engine. Unfortunately I was looking closely for a spark and I was literally showered in petrol. Long story short, I checked the dipstick and petrol was very nearly up to the top, way past the full mark. Today I pulled the sump plug and got over a gallon of mainly petrol mixed with the engine oil out of the engine. Somehow petrol has been getting into the sump - lots of it !

    It appears that this engine has a pulse style fuel pump (not come across these before) Apparently it sucks fuel out of the fuel tank on the downward stroke of a piston and then pushes it into the carburettor on an upward stroke of a piston. Presumably there are some valves in the pump which aren't working as they should and herefore allowing a lot of petrol into the sump.

    It's all I can come up with - does anyone else have any other ideas please ? TIA for any help.

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    Re: Kohler vee-twin 20hp petrol.

    The fuel pump could have a perished diaphragm allowing fuel back down the vacuum tube and into the sump,or,and I think it will be more likely,either the float in the carb has stuck or the needle valve that it operates isn't sealing shut.......worn seat or bit of dirt maybe.

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    Re: Kohler vee-twin 20hp petrol.

    Quote Originally Posted by agrimax View Post
    The fuel pump could have a perished diaphragm allowing fuel back down the vacuum tube and into the sump,or,and I think it will be more likely,either the float in the carb has stuck or the needle valve that it operates isn't sealing shut.......worn seat or bit of dirt maybe.
    Mmmmmm, hadn't thought about that. I suppose it could also be a damaged/punctured float. Thank you. I've just been watching some videos on YT and I think I will test the pump first by blowing and sucking on the vacuum tube, if I can either get it off where it goes into the crankcase or, if I've got a piece of tube the same size that I can put over the plastic pipe that comes out of the pump.

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    Re: Kohler vee-twin 20hp petrol.

    Quote Originally Posted by agrimax View Post
    The fuel pump could have a perished diaphragm allowing fuel back down the vacuum tube and into the sump,or,and I think it will be more likely,either the float in the carb has stuck or the needle valve that it operates isn't sealing shut.......worn seat or bit of dirt maybe.
    Quote Originally Posted by zaza View Post
    Mmmmmm, hadn't thought about that. I suppose it could also be a damaged/punctured float. Thank you. I've just been watching some videos on YT and I think I will test the pump first by blowing and sucking on the vacuum tube, if I can either get it off where it goes into the crankcase or, if I've got a piece of tube the same size that I can put over the plastic pipe that comes out of the pump.
    i think it'll be like Agrimax said.

    On Briggs & Stratton Pulsa-jet carbs they have a sheet diaphragm a spring pushes on and the crankcase pulsations makes the diaphragm pump fuel, close by using the same diaphragm sheet are two tiny flaps that simply act as the oneway valves required to pump fuel.

    I'm guessing the Kohler setup may be similar in principle? one issue I can think of is these V twins are horizontal and the carb may be low enough for simple gravity drain with a full tank and iffy float/needle. I bet its also like a lot of todays throw-away designs that there may not even be a shut off tap that would be handy when there's a problem.
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    Re: Kohler vee-twin 20hp petrol.

    There have been some developments. I took the pipe off the pump that goes to the crankcase and substituted a short piece of pipe in it's place. I then took the pipe off the pump that goes to the carb. and substituted another short piece of pipe in it's place. I left the pipe from the fuel tank still attached to the pump.

    I then alternatively sucked and blew down the pipe that I had substituted for the pipe that goes to the crank, thereby mimicking the action of the crankcase pressure. The result was that small amounts of petrol were emitted out of the pipe that was replacing the one that normally goes to the carb. And I didn't get any petrol in my mouth and so I reckon that the pump was working as it should.

    The Kohler is a vee-twin, not horizontal and thankfully there is a shut-off tap under the tank.
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    Re: Kohler vee-twin 20hp petrol.

    Even more developments. Today I attached a piece of pipe to the intake pipe that is normally fed by the pulse pump. I then put a squeezy bottle containing petrol onto the other end of the pipe, inverted the bottle and applied pressure. There was petrol streaming out of the carb, proving that the float arrangement/needle valve wasn't working as it should. So I took the top off the carb. c/w with the pipe and held it over some water in a dish and then pressurised the pipe by blowing into it. Sometimes I could get bubbles out from under the carb. top, sometimes the float was obviously pushing the needle valve up onto it's seat as it should.

    So I dismantled the needle valve and it looked O.K. but there was some crud in the bottom of the float chambers and so I cleaned everything up and put it back together again and repeated the test with the top back on the carb. This time, when the float had risen sufficiently it closed the needle valve and I couldn't pump any more petrol into the pipe. I think I will try and start it again when I get a couple of spark plugs that I have ordered but I am beginning to think that there was some crud that was stopping the needle valve from seating properly. And if I'm honest, I don't think the fact that the needle valve is spring loaded helps the situation.
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