OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Flooding in Briggs and Stratton

In a Masport mower
B&S Quantum XM 50
Model 12F802 Type 0842 -02
Code 95051059

I had a fuel starvation problem and cleaned carby removing junk from the bowl and main jet. Re-assembled and the machine ran well but overnight flooded/leaked badly.

Replaced the seat and needle valve with new parts as seat possibly looked suspect so was a likely culprit. New gasket too.

Left it for some time and found a fuel leak from the port arrowed in the pic below. This is open and does not look as though it has had a plug in it.

Can anyone help with any suggestions please? This has caused me a great deal of angst as I have had the thing apart so many times.

Thanks folks, I'd be most grateful for any ideas.

Hi there, check the float dosnt have a hole in it. Check it by submerging it in some fuel for half an hour or so and take it out and shake it, if theres fuel inside then theres your problem. If the float is ok then flooding out would still suggest a bad needle and seat so even though you've replaced them check them by trying to blow through the fuel inlet with the float and needle in place while holding the carb upside down.

Thanks bigted.
I'm pretty sure the float is fine, but the needle may still not be seating well. I am still trying to sort it.
Thanks again.

Another thing to check is the float pivot pin. If the float is not completely free to pivot on this pin, the float system will not work properly. By the way, the port you are referring to is the bowl vent and joins up with a small hole in the underside of the carby above the float. It allows atmospheric pressure into the float bowl to maintain correct fuel level.

vwq47, you didn't by any chance put the new seat in that Walbro LMS carburetor upside-down did you? If you have the version that has an all-metal needle, it uses a Viton seat. The seat has to be installed with the concentric circles upward toward the carburetor, not downward toward the needle. (There is also a less common version that has a Viton sealing area on the needle - that type uses a metal seat. If you replace both needle and seat as a pair all is good, but if you use a non-matching needle and seat, it may flood.)

Thanks Folks.

The pin moves TOO freely in that it readily falls out on dismantling. In other machines I have worked on there has been a bit of friction in the mounting post holes.

I was lucky that I put the seat in in the correct orientation - though did this on gut feel rather than having been able to find info.

In the end, and in desperation, I wondered whether the needles were the same - they sure looked it. When I took the new one out (again) and compared it with the original (which was apparently in perfect condition) I found that the new one was about a millimeter shorter than the original one! Hoping against hope that this was the issue, I put it back together using the old needle. I reasoned that a longer needle might cause sufficiently more pressure at the seat to make the seal.

It worked!

Beats me why a genuine part would differ from the part in the mower to start with. The local mower shop and I independently identified the B&S part number.

Folks, Thanks again for your help here. I sure will keep perusing the board.

vwq47
downunder

As you said, the longer needle together with the new seat would have made the float lever geometry different, which might have caused the float to exert more closing pressure on the needle against the seat. However if you bought the new needle and seat as a set, and they matched your carburetor model, they should have worked. Perhaps your rather worn float pivot has developed a favourite place to sit, and binds a bit when it has to operate in a different position. Alternatively, the needle and seat you bought might have been intended for a different version of the LMS carburetor.

I'm glad it's fixed, vwq47. I'll close this thread - if anyone needs to post to it, just PM a moderator.