I see these engines all the time on consumer grade lawn tractors: the 17.5 HP Briggs & Stratton single cylinder verticle. The model in question is 31P677-3373-G1. This thing is not acting like all the others, for some reason.
The customer complaint was that she could mow for about 15 minutes, and then it would sputter and die. She tried to choke it, and that would prolong the running for a few seconds, but that was it. The first time I got it, I replaced the carburetor, because it was running extremely lean all the time anyway, loaded and unloaded. It seemed fine when I tested it, so I thought that was that. But she called me back a couple of days after I took it back to her to tell me that while it runs better now, it still dies after 15 minutes of mowing. She lets it sit for about 5 minutes, and then she can get about 4-5 more minutes of mowing out of it before it conks out again.
I know what you all are thinking: ignition module. But I don't think so. When I test ran it last week, it died, acting like it starved for fuel. When I pulled the gas line from the carburetor, no gas was coming out of the line (this is gravity fed from the tank). I blew back through the line, and then gas started coming out. So I removed the tank, made sure it was clean, replaced the fuel line and filter (with an OEM 691035 filter and 792020 gas line), and made sure the elbow coming from the tank was clear. So everything in the fuel system was new: line, filter, tank (cleaned, not new), and carburetor. I also replaced the spark plug (which was a Briggs branded plug - perhaps the original one) with an NGK CS6 (1716).
I was testing it again this morning, and it ran good & smooth for several minutes. Then eventually (after about 35 minutes of running, 20 of mowing), it started to sound like the engine was laboring slightly, more than it should be I thought, but it kept going. Then it started to sputter and act like it was going to die. All I did was slow the tractor down, to reduce the amount of load on the engine, and it revived and continued running for a few more minutes, during which it would act like it was starting to stumble intermittently. After a few more minutes of this, it was consistently running kinda rough, like it was cutting out. Then it started to die, and when I stopped the PTO to reduce the load on the engine, it was still wanting to die. So I shoved the throttle all the way up to choke the engine, and it limped its way to the shop. Then it finally died then, and I could not get it to run any more.
I took the gas line from the carburetor again, and nothing was coming out. I removed the gas cap, wondering if there had been a vacuum pulled on the tank. But still, nothing came out. Then I blew back through the line, and then gas started to come out. What's going on here? I thought the section of fuel line from the filter to the carburetor felt pretty hot to the touch. Am I getting some sort of vapor lock? I hardly EVER have problems related to vapor lock. Do I need to wrap some kind of insulation around the fuel line to keep the gas cooler? I see these engines on these kind of cheap lawn tractors all the time, and none of them have this problem. What ideas do you have?