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Old 12-26-2013, 03:16 PM
BryanStein BryanStein is offline
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gas in oil JD 757 Kaw FH721D 21 hp engine

Bought a rebuilt mower 2 yrs ago. Carb was not rebuilt. It wouldn't crank after first use because it wasn't getting gas. I cleaned the carb and solenoid valve. Ran great the rest of the summer.

This year I have to pour gas in the intake to get it to start every time. I'm a homeowner that uses it once every two to three weeks.

About halfway through the summer I noticed the oil smelled like gas, but was not over full. So, it's not losing much gas into the oil. I started to order a carb rebuild kit, but thought it could also be the solenoid. It's obvious the carb, or even the fuel line, is being drained of all its gas. That's why it takes so long to crank. It will actually run a full battery dead without cranking. That's why I pour gas into the intake to crank it.

Guys, which could it be. I think the solenoid is just a safety valve that cuts the fuel off from getting into the carb when the switch is turned off. Even if it doesn't turn off, it wouldnt cause gas to get into the engine would it? That just keeps gas from getting to the carb.

Isn't the carb float and needle what ultimately stops the flow of gas into the engine? But if the solenoid valve is working, how can the carb get enough gas to flow into the oil.

How do I test the float and needle, and how do I test the solenoid valve. A carb kit is cheap. A solenoid valve is not. Your help is greatly appreciated. It is forums like these that restores my faith on the goodness of the world. I'm a member of other forums that save people thousands of dollars on deisel engine repairs.
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Old 12-26-2013, 04:18 PM
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dutch1 dutch1 is online now
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The solenoid serves only to prevent "dieseling" or "after run", when the switch is shut off. Even if the solenoid is operational, it won't prevent fuel from running into the crankcase--but you can check the operation by touching one of the two leads to 12V+ and the other to negative.

It's possible that you may have some debris that is holding the inlet needle open or you may have an inlet needle that will not hold pressure. It's been a while since I've been into a 721 carb so I don't recall if the float is hollow in nature--if it is, check to see if it may retain fuel which will not allow the inlet needle to shut off fuel.
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Old 12-26-2013, 06:17 PM
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BigFish BigFish is offline
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To expand upon what my esteemed colleague Dutch said.... The solenoid valve, AKA anti-afterfire valve, acts to prevent the fuel from entering the MAIN JET ONLY. It has no bearing on the fuel entering the FLOAT BOWL. That is controled by the inlet needle/float. If the inlet needle is not sealing, then the bowl will fill up completely and overflow into the intake and thus enter the crankcase. Not good!
So you need to get into the carb and see whats goin on.
It's also a good idea to install an inline fuel shut-off valve for good measure.
I usually install one on my customers units.
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