'86 Lawn Boy F Series - Fuel Leaks From Intake?

16 years ago

Hey everyone! I had no idea there was such a following for the Lawn Boy push mowers out there, but alas, I've become a follower as well. This mower cuts better than anything I've ever used in the past, and I've had a lawn care business going for 15 years, all run with 4 cycle Briggs and Tecumseh mowers.

I had two Model 6430 LB's donated to me last year, and just rebuilt the carb on one of them. I replaced the float, needle and seat, filter, and every other replace-able part It fired up great and I adjusted the carb a bit to get it to run smooth. It cuts well, has great power, and doesn't smoke or emit a large amount of fumes.

The problem I'm having is that fuel will pool in the bottom of the air filter housing when the mower's been run for a period of time, and the fuel will leak out onto the deck.

Does anyone know what could be causing this? Reed valves? Clogged exhaust backpressure? I'm taken the engine off the deck and I'm willing to get down in there and replaced whatever needs it.

Thanks!

Justin

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Comments (7)

gorper99
16 years ago
Use the fuel shutoff when you are done-then run it dry?
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jsoluna
Original Author
16 years ago
It doesn't leak when it sits, only when it runs.
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I know - its the kind of thing I like to do too. Sounds like the deck is okay. I would keep on using it. CD pack failures are irritating, but when you consider that most people have to buy a new mower long before 9 years, it seems very cheap to operate. Even if you have put new wheels and axles on at about the same frequency as the CD packs, you really are not spending any money on it. And, you can still find the rear-bagging kits and deck plates (blank for discharging, blocked for mulching). Other things you may encounter after such long service are crankshaft end seals popping out or just leaking, the need to rebuild the carb and carbon build-up in the exhaust ports and muffler. I always recommend adding Marvel Mystery oil to the gas in addition to your regular oil mix as well as the use of a fuel stabilizer. If you use Ethanol-blended fuel, get the Stabil Marine for Ethanol Fuels. All engines like MMO, in particular the 2-cycles.
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While a plugged muffler or plugged exhaust ports will keep a LB from running right, it will not keep it from at least firing a few shots. Engine couldn't possibly have run to that point. Cleaning the muffler depends on WHAT muffler your LB has. The one pc. steel ones can be thrown in your charcoal grill when you have finished cooking and left. Tap/blow out when cooled. The muffler for the model number given is a 2 pc. cast aluminum one which easily comes apart for cleaning. Use some SeaFoam in your fuel for a few tanks full. Your trouble could be a lot of things. That model is the first one with CDI which continues to be a weak spot with LB. However, you say you have good spark so shouldn't be that. Could be bad crankcase seals or bad reed valves. Walt Conner
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Mike72
16 years ago
Assuming the needle and seat are sealing and the float level is correct this is not unusual with a F engine.It happens from the combination of too much reed clearance and sustained high rpm. Reeds tend to get bent slightly open with long use allowing a tiny amount of reverse flow before closing on the piston down stroke. Now there is a fuel fog which is present in the carburetor of all reed engines, even when new and this tiny amount of reverse flow pushes this fog closer to the air cleaner end. The degree of this fog depends on the condition of the reed and how quick it closes. High rpm aggravates the condition creating a fog that will reach the air filter and soak it. Check the maximum rpm and adjust if necessary, but you probably will need to replace the reed. I think Lawn Boy made a plastic part that was made to fit in the carb to help control the fog, but I don't know the part number or if it will fit your carb. Also check the exhaust ports if you haven't done it in a while.
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jsoluna
Original Author
16 years ago
Yeah, I've got the engine removed for rebuild now, and was figuring that the reed valves were a bit worn, even though upon inspection I couldn't see that they were too bad.
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rdaystrom
16 years ago
Agree with the above diagnosis. Replace the reeds.
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1saxman
16 years ago
Also check to see that RPM does not exceed 3200. If it's running faster that would aggravate the condition.
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jsoluna
Original Author
16 years ago
Thanks guys. I only had the engine running at low-mid throttle, and I'm pretty sure it wasn't running to fast.

I'm headed over to the mytractor forums to chronicle the rebuild if you're at all interested in pics, etc!
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'86 Lawn Boy F Series - Fuel Leaks From Intake?

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'86 Lawn Boy F Series - Fuel Leaks From Intake?

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