Lawn tractor won't crank

[suemarkp]

I have a Sears lawn tractor with a Koehler engine. I've been having trouble starting it lately. The starter makes a Whump noise, but the engine won't turn except for an initial few degrees. I thought it was a weak battery, but I'm not so sure now, as I've put a charger on it and tried start it with that. It seems like either the engine is too hard to turn, or there is a bad spot on the starter. I can see a huge current draw from the starter if I hold the key in start, but the starter is not turning.

Today, an interesting thing happened. After the initial WHUMP, I noticed fuel leaking onto the ground. There was a huge amout of fuel dripping off the bottom of the engine. I thought the fuel line was loose. But it was coming out the muffler pipe. It eventually stopped dripping, but the engine still wouldn't start. After enough attempts (about 20 tries over 10 minutes), eventually the starter turns and the engine starts and runs fine. Restarting is always easy, its only when the tractor has sat for a few days that it has this problem.

I have also noticed for the last 6 months, that a rather large wet spot is made by the exhaust pipe when the engien first starts. Today was the first time a stream of gas came out of the muffler instead of just an initial spray.

Any guesses as to what is wrong? A sunk float, or a leaky needle valve? Would having some fuel sitting on top of the piston make the engine hard to crank?

[Ohm1]

May have water in your fuel tank. Make sure you turn off your fuel value after use. During the winter, it wouldn't hurt to remove the fuel.

This based on a simular problem I had with my mower. May be something else!

[suemarkp]

It has no fuel shutoff valve, and that would perhaps reduce pressure on the float so it wouldn't flow into the carb if the needle valve seals poorly. I may add a shutoff valve if I can find one to plumb in line.

Why would water in the fuel prevent cranking??? This is usually an issue if the tractor has sat for a few days or longer. I usually use 3/4 of a tank every time I cut grass, so hopefully there is no water in the fuel. I don't usually have any additional problems with the spring startup, and I try to start the tractor every month or two in the winter and let it run for a while.

[mdshunk]

Your carb is leaking fuel into the open cylinders. That "whump" is because you're compressing a cylinder full of liquid fuel instead of air and a fuel mist. This can bend valves and break parts if you don't get it corrected. The cylinder's oil rings will also not hold back fuel, so you surely will have an unusually high oil level because you'll have lots of fuel in the oil. I've got an old tractor that leaks like this when it sits for a few weeks. My corrective actino was to shut off the fuel line from the tank rather than have the carb rebuilt. It works fine otherwise, but just weeps fuel through the carb at a slow rate while it's sitting between uses.

[suemarkp]

Thanks, that's is what I thought may be going on. The oil is a little high, and I don't know the orientation of the piston -- the intake seems to be on the top of the engine and the exhaust is on the bottom. So I was hoping fuel would run out the exhasust valve. But I suppose I could have unlucky valve timing and fill the engine with the exhaust valve closed and the intake open.

I tried starting it this morning and it cranked longer, but wouldn't start. It would backfire and I was feeling some intermittent recoil and resistance during the starting process. Perhaps this was compressing gas into the cylinder head and bending valves...

Looks like I need to find a shutoff valve.

[Bumblerazz]

May I suggest that you may also have liquid fuel on and/or around the spark plug. Fuel getting to the muffler usually means that the engine is "flooded" (as mentioned by the others) and a wet plug won't spark. If you can remove and dry the plug before the starting process, it may start sooner / easier.