So it's not a lawn mower but hopefully someone here will have some advice. I purchased a one ton mini excavator with a B&S XR 13.5 gas engine. The issue I'm running into is bubbles in the fuel tank and the tank pressurizing to the point that it blows fuel out if I take the cap off after running it for about 20 minutes. The unit does get fairly hot and of course we've had a string of 100+ degree days (It was 104 outside when I noticed this problem). I don't necessarily feel like the fuel cap is venting properly but I assumed the fuel system should be under vacuum on a gravity system and not under any positive pressure. I'm going to try another fuel cap but want to have some input if anyone has any other ideas on things to check especially since it continued bubbling once the cap was removed.
2023 Briggs & Stratton XR 13.5 - Bubbles in fuel...
- Thread starter jthrash
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Model # - 25T237-0085-F1 (according to B&S website, I can't see a tag with model number or serial number on the engine itself)
JF 420-209-23033102-Y43 is stamped on the inside of the cooling fins on the cylinder.
Engine Family: PJDGS.4202UA according to Emission Control Information decal on fuel tank.
VegetiveSteam
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Was the engine running when you took the video? I assume it was but I couldn't tell for sure. If so then the bubbles are normal and caused by engine vibration. Years ago manufacturers would put baffles in the fuel tanks to help limit that but then the baffles could deteriorate and plug the fuel outlet. If that video is with the engine not running, that fuel is getting a lot hotter than it ever should IMO.
As far as pressure in the fuel tank, that should never happen and enough pressure could cause carb flooding. That would make me think the fuel tank is not venting properly. From the parts breakdown it looks like the engine has a fuel cap with a carbon filter in it so as to not vent fuel vapors into the atmosphere. That's pretty common these days on engines with fuel tanks mounted on them. Typically those types of caps have a tether on them. If that's the case then replacing the fuel cap should eliminate the pressure you're finding when you remove the cap.
The fuel tank should be designed to keep the fuel level low enough so it doesn't contaminate the fuel cap but with a little effort you can fill the tank all the way up into the filler neck. If those carbon filter fuel caps get fuel in them that can deteriorate the carbon and plug the vent.
As far as pressure in the fuel tank, that should never happen and enough pressure could cause carb flooding. That would make me think the fuel tank is not venting properly. From the parts breakdown it looks like the engine has a fuel cap with a carbon filter in it so as to not vent fuel vapors into the atmosphere. That's pretty common these days on engines with fuel tanks mounted on them. Typically those types of caps have a tether on them. If that's the case then replacing the fuel cap should eliminate the pressure you're finding when you remove the cap.
The fuel tank should be designed to keep the fuel level low enough so it doesn't contaminate the fuel cap but with a little effort you can fill the tank all the way up into the filler neck. If those carbon filter fuel caps get fuel in them that can deteriorate the carbon and plug the vent.
The engine was NOT running when I shot that video and the machine was definitely hot. I've been contemplating installing a fan in the rear of the excavator to help draw heat away from the engine. It's super compact and I'm not sure that there's enough air circulation for this machine to properly cool in this deep south heat. It'll be nice in the winter but it's rough right now. I included a picture of the machine just for reference of available air flow. The engine, tank, and hydraulic system are all under the seat and floorboard.
I ordered a replacement cap yesterday using the B&S part number because I had the same thought of flooding due to pressure. It looks slightly different than the one that is currently on the engine but I'm hoping that is the difference between one sold in China and one sold in the US. The machine only has 3.9 hours on it so it's possible the cap was just faulty from the factory. It ran fine through the first couple tanks of fuel and after the last fill-up is when it began stalling and shutting down after about 20-30 minutes of run time and usually only when under a load and hot. It's just a strange scenario that I've never encountered. Hopefully I can find some resolution fairly quickly. This is a handy little machine on our land.
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VegetiveSteam
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What does the spark plug look like? Does it show signs of the engine running hot?
Hammermechanicman
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You are boiling the fuel in either the carb bowl or fuel line and it bubbles back into the tank on a gravity system. It is way too hot.
Sounds like a fan to pull some air through the confined space the engine is mounted in is probably my solution at this point. I don't know any other way to dissipate the heat from around the engine. I'll measure the area I've got to work with while I'm checking that spark plug this evening and see what I can come up with to make it work.