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General Category => General Discussion => Topic started by: brider on May 10, 2024, 08:43:00 PM
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I bought a used DR mower with a Briggs vertical-shaft engine with side-mounted carb. Typical lawnmower-type configuration.
I discovered after letting it sit for a few weeks that the crankcase had filled with gas. There is a shutoff valve on the line from the tank, but honestly I have never used a shutoff in a similar configuration and have never had a sump fill with gas. What is the mechanism that will allow gas to fill the sump?
I assume a bad needle/set allowed the gas to overflow the bowl and run down....where? If it ran past an open intake valve, wouldn't it have pooled on top of the piston & caused a hydro lock when trying to start? Or would it have flowed past the worn rings into the case? After discovering this AFTER I tried like hell to crank it forever to get it to fire, my gut tells me I caused some significant internal wear.
It started and operated well enough to drive it up ramps and into my truck, then back down the ramps when I got home and around the edges of the yard to test it out. I suppose a carb rebuild kit or even a replacement carb is cheap enough, might try that with a fresh change of oil.
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Yes,Brider It would have to flow fuel past the needle valve and through the intake tract to the cylinder, and down past the rings ,into the crankcase. A piece of dirt in the needle valve/seat? Clean and rebuild the carb, or replace it with one of the cheap replacements available online. An inline shut off valve can also be installed for extra peace of mind. I had the same thing happen with a craftsman power washer, with a B&S vertical shaft engine. I added a shutoff valve,and fuel filter inline.
Rick.
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As BBRick said, adding a fuel shutoff valve is necessary, and a fuel filter is cheap protection. I like the clear filter John Deere filters, because then I can see fuel passing through, so I know fuel flow is ok.
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Another thing to check. On the side of the engine there should be a fuel pump. It has a inlet, outlet, and a hose that goes to the crankcase. [most likely to the valve cover on a briggs] Make sure that line is not wet with fuel. Ive seen those pulse pumps leak, and suck fuel into the crankcase. If the tank is higher then the carb you really need a shutoff. and also a fuel filter would be a good addition if it didnt have one. I would also rebuild the carb before replacing with a aftermarket if possible. If its a vtwin they are a bit of a pain. You need to remove the intake to get to it. Also if it is a twin, it might have a plastic intake, and you need to make sure is seals when you put it back together, because they warp. If its a single cyl its eazy peezy.
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The piston rings are far from a great seal for something as light as gasoline. Though the intake valve should do a good job of sealing IF it is closed.
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Everyone I know who has one in my neighborhood has the little inline shutoff valve installed. They all leak eventually.
It is a Briggs part , most always hanging on the rack with the filters and such at most any big box outlet. Just cut the fuel line in a convenient place and stick it in there.
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Pay close attention to the float. Stuck needle valve will allow unrestricted fuel flow but if the float doesn’t float the needle valve never seats. If the float is brass you can shake it and you’ll hear fuel sloshing around in it. If it’s phenolic it can become saturated. Test it by seeing if it floats in a container of gas. Best to just replace it
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The piston rings are far from a great seal for something as light as gasoline. Though the intake valve should do a good job of sealing IF it is closed.
Most modern L&G engines have vary poor sealing valves even new. Even brand new replacement head, with valves and all seal badly in most cases. Maybe its just that the springs are so weak. I work in the field, and Any time I have one apart, there needs to be time for lapping the valves. They seem to run fine mostly.. Just low speed, low power, and low compression I guess.
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Thanks, all, it sounds as simple as I suspect. Also note that in my OP I state there IS a shutoff valve, I just didn't use it, and the PO didn't point it out. I have a push-mower I use for trimming, and a logsplitter, BOTH with vertical-shaft B&S engines and neither one has a shutoff in the fuel line and each are over 10 yrs old and I've never encountered this. Thus my inattention to the DR mower engine. They're both probably leaking into their sumps as I write this.
I wonder what kind of damage I did to the engine trying to crank it to get it to fire (which it did, a few times).
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Thanks, all, it sounds as simple as I suspect. Also note that in my OP I state there IS a shutoff valve, I just didn't use it, and the PO didn't point it out. I have a push-mower I use for trimming, and a logsplitter, BOTH with vertical-shaft B&S engines and neither one has a shutoff in the fuel line and each are over 10 yrs old and I've never encountered this. Thus my inattention to the DR mower engine. They're both probably leaking into their sumps as I write this.
I wonder what kind of damage I did to the engine trying to crank it to get it to fire (which it did, a few times).
If it cranked over freely, and you didnt run it for hours, its fine. These are forgiving engines. As I said, I work in the biz, and MAN you should see some of the heeps that come in, and the abuse they have suffered, and with a little work they are running like new. Most issues I see with needing the shutoff are in transporting it. The shaking around causes them to flood. Just sitting, and it does it you have a issue somewhere else.