8.5 HP B&S Engine just dies!

[knute_m]

This spring I inherited an Arens 927 series rear-engine mower with an 8.5 hp Briggs and Stratton engine.

Although it is probably about 10 years old, I doubt it has 75 hours on it. For the past three or four years I'd use it a couple of times per year with the dual bagger to clean up my in-law's yard. After each use, I'd either run all the gas out of the engine, or add Sta-bil to it. I also changed the oil each October.

Anyway, I brought it to a 2nd home we own where I have about an acre-and-a-half lawn to mow. Each time I've used it, the engine has died after it has been running about a half-hour, or so. It acts like it runs out of gas. If I try to start it, it will run for a couple of cycles. The longer I let it set, the longer it will run. If I wait about five minutes, it will usually start and run for another half hour, or so. On Saturday, it did its usual routine once. When I was almost all done, it died again, and would not restart even after about a half hour. I put it in my truck. When I got it home, I decided I'd try to work on it. It sat in the truck for maybe an hour or so before I tried to start it. It started instantly, and I mowed with it for about 45 minutes without problem.

From working on it about five or six times since May, this is what I know:

It has great spark (including, when the engine will not start). The spark plug looks like the carburetor must be set properly -- not fouled, not white, just right.

About the second time this happened, I pulled the carburetor off, and pulled it all apart. I couldn't find anything that even looked suspicious. I put it back together. I had the same problem the next time I mowed.

When cold, it starts instantly. I idles perfectly. It has plenty of power and does a great job of mowing when it is running.

I've pulled the muffler. Everything is clean.

On Saturday when it quit, I loosened the screw at the bottom of carburetor float housing. The gasoline that came out was really hot. It may be that the black gas tank was just heated from the sun (it was sunny and close to 90), but the gas line runs through a bracket that it part of the muffler. The carburetor is right next to the muffler. I'm wondering if I'm experiencing some kind of vapor lock -- but even after I ran gas out the float housing, it still would not start.

Does anybody have any ideas? I'm already bald, so I have no hair to pull out.

Thanks in advance,

Knute

 

[Egon]

There just may be a capacitor in the ignition circuit that fails when it's hot. Had that happen on an 8 HP B&S. Worked like a charm cold. Then stopped as soon as it got hot.

Can't give any advice on how to find or change it.

Egon

 

[knute_m]

There just may be a capacitor in the ignition circuit that fails when it's hot. Had that happen on an 8 HP B&S. Worked like a charm cold. Then stopped as soon as it got hot.

Egon

Egon,

Thanks for the note. That was one of my early guesses. But, I seem to have good spark even when the unit will not start. (I edited my post by adding that tidbit after I read your note). If the thing is in its non-starting mood, I can pull the spark plug, ground it, and get a good blue-white spark when turning the engine.

Thanks,

Knute

 

[waynokakid]

I had a similar problem on my 12hp B&S riding mower. Couldn't figure it out for the life of me. It would run fine for about 1/2 to 3/4 of an hour. Then would sound like it was running out of gas. And finally die, then not start till next day. It had plenty of fresh gas and clean filter. Good spark. Finally took it to a friend who does small engine repair. Found out the muffler was loose, causing hot exhaust to reach the carb! New muffler and works fine now!. Sometimes simple things are hard to find.

 

[BobRip]

Perhaps the vent on the gas cap is clogged. It this happens a vacuum builds up in the gas tank and gas no longer flows out. It might work (as a test) to loosen the gas cap after the engine dies. See if it starts and runs then. I have not seen this but others have.

Bob Rip

 

[ejtaylor822]

Echo BobRip with the vacuum in the fuel system. Also, do you have a "see-through" fuel filter? Can you tell how much fuel is in there when it starts coughing?

I had very similar situation to yours after I replaced the fuel filter on mine. It started the week AFTER I replaced the filter - as I filled the tank and ran it the day the filter was repalced. But, when the tank got low, the next week, there was not enough pressure to get the gravity fed fuel to the filter & carb. Turns out, that when I replaced the fuel line from the carb to the filter, I cut it too short. This had the filter level or slightly higher with a bend coming out of the tank - tank is full ran great, half to empty - coughed and would die. Making it worse was the clogged vent in the fuel cap.

Good luck, its aggravating.

Eddie

 

[waynokakid]

You got me there BobRip. That is usually the place I check first when I fuel up! I had that problem too, the vent cap was wore out and would stick closed. I replaced the whole cap and it works fine now. It will sound as if the motor is starving for fuel and then finally die.

 

[knute_m]

I had a similar problem on my 12hp B&S riding mower. Couldn't figure it out for the life of me. . . . Found out the muffler was loose, causing hot exhaust to reach the carb! New muffler and works fine now!.

Thanks to all for the ideas and suggestions. On the way home from work tonight I plan to buy a new muffler and a long piece of gas line.

The muffler that is on there has some rust, and if I finish up mowing when it is almost dark, I notice it has a dull red glow. It seems to run hotter than it should, and being within about an inch of the carburator float bowl, it certainly could be the culprit. It's worth a try.

As several have suggested, it does seem to have to do with gasoline flow. Early on, I pulled the gas cap and made sure there was plenty of air in the tank. Even on Saturday, when it last gave me grief, I filled the gas tank after it died the second time. When it died, it was about half-full. Filling it didn't help.

If it has a fuel filter, I can't find it. There is just a hose that runs from the bottom of the gas tank to the carburetor -- right over the muffler. As Eddie said, his gas line ended up being a little short, and mine looks pretty tight. That is why I'm going to replace it too.

The gas tank has baffles in it, and I can't see the inside bottom. Over the past three gas tank fillings, I have run a full bottle of STP carburetor cleaner/water-eater, etc., through the tank. While in its bad mood, I've pulled the gas line off at the carburator, and it pours out what appears to be very clean gasoline. Same with removing the screw at the bottom of the float bowl. As I mentioned above, the gas sure seems to be hot.

Anyway, it is time to head home, and stop for a muffler on the way.

Thanks again,

Knute

 

[cup149]

I had the same thing happen on a 5hp Briggs. It turned out the exhaust valve clearance was too small. As the engine heated up, the valve got longer and would be held off the seat, causing the engine to quit untill it cooled a bit, then it would start. Grinding the valve to the proper clearance put it right, been running it for two more years.

 

[nysdotinspector]

I"ve had a similar problem with a briggs engine myself a few years back, and after trying everything I noticed that the carb pushed on a tube that acts like the manifold and inside the carb was a -o- ring that makes a seal. I found this out by spraying some carb cleaner at the connection and it would run fine. I changed the -o- ring and that solved the problem. Good luck. Vern