leaky Walbro LMT carb


Old 10-29-08, 09:30 AM
Thread Starter
Join Date: Oct 2008
Location: Ohio
Posts: 3
leaky Walbro LMT carb


I bought myself used Murray ride-on, and midway through my first mow, the carb flooded out (i.e. all fuel in tank through the carb/airbox/etc...didn't catch it until the next day). I disassembled the carb, replaced the needle valve, since I assumed that this was likely the problem. After reassembly, the mower sat for 2 weeks without any issues. About half way through the next mow (I'd shut the engine down and was dumping grass), the carb flooded again. Ever since then, I can't get it NOT to flood. I've pulled the airbox off and can see gas flooding into the carb body through the jet? (port in the middle of the carb body as you look inside). My local repair shop guy was kind enough to throw in a new valve seat, so I've got a new needle/new seat...but still have the leak.

The engine is a B&S 289707 something or other, with a LMT Walbro carb. I'm at the end of my rope on this...can someone point out what I'm missing, or something else to try? Is there any potential for that main jet to clog in an open position? Would a soak in some parts cleaner help that?

Appreciate any suggestions anyone can provide.

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Old 10-29-08, 01:10 PM
Join Date: Oct 2008
Posts: 19
It sounds like the float. Take the float off, and shake it. If theres fuel in it, you have found your culprit.
Old 10-29-08, 02:20 PM
Thread Starter
Join Date: Oct 2008
Location: Ohio
Posts: 3

I'd thought the same as well during some earlier troubleshooting. The float's dry as a bone...have also run this down to a local shop and had the carb tested...it supposedly holds 2 psi (??) air as well as gas (are they just running some light air pressure down the fuel line to check if the float is seating? is 2 psi a good #?), but as soon as I get it home and installed, thar she blows.
Old 10-29-08, 03:56 PM
Join Date: Jun 2006
Location: St. Louis
Posts: 2,365
I had a similar problem which end up being caused by the old fuel line. When you remove the bowl the next time check to see if there is some tiny black residue in the bowl. If that is the case you will most likely need to replace the seat again along with the fuel line, in my case I replaced the fuel line and it happened again which was caused by the residue that was setting behind the seat that I couldn't flush out with the seat installed because of the seats restricted flow. Have a good one. Geo
Old 10-30-08, 04:24 AM
Join Date: Feb 2008
Location: usa
Posts: 755
Check and replace the fuel line as Geogrub recommended. Fuel lines deteriorate and debris can prevent needle from seating.

Briggs and Stratton states, “The inlet needle should pop off and re-seat at 2 psi or greater.”

I suggest you remove the float and needle and polish the needle, needle cavity and seat. Deposits on the cavity wall or needle can intermittently cause the needle to drag and not fully seat. Use a cotton Q-tip saturated with metal polish and thoroughly clean and polish the needle, needle cavity and seat.
Old 10-31-08, 07:41 PM
Join Date: Jul 2005
Location: Texas
Posts: 205

When you replaced the needle and seat,did the seat have a groove on one side,if so check the seat,the groove goes down in the carb,or maybe the seat is not all the way down in the carb.Just my 2 cents.

Old 11-03-08, 09:10 AM
Thread Starter
Join Date: Oct 2008
Location: Ohio
Posts: 3

Thanks for the help. Since I originally posted, I have:

- brand new needle (this is the 2nd brand new one)
- brand new seat (again, the 2nd new one)
-- seat was installed at the dealer, so I can only guess they got the grooves/orientation correct. ditto on the seating depth...looks good to me, though.
- carb soaked for the prescribed 15+ minutes in parts cleaner and then thoroughly blown out/cleaned...looks great
- brand new fuel line, in-line fuel filter
- all new gaskets throughout the carb
- just for S&G's, dunked the float in gas and weighted it down for good measure...after 2 hours, not a drop inside

After everything, post-rebuild and install...it still leaks. So, I cheated and installed an inline shut-off valve...and tests confirm: flipping it on just prior to start allows for a nice smooth run, and then flipping it back off (of course) stops the leak. Not the optimal solution, but I'm throwing in the towel.

Again, I appreciate the help.



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