Gas leaking from carb from ports alongside valve choke

woodchuckcanuckAugust 17, 2008

IÂve been trying the last three days to fix my lawn mower. I have a Craftsman Rotary Lawn Mower Model Number 944.367742, B&S 4cycle engine Model Number 126T05-0880-B2.

Mower is 2 years old and has 15 hrs of running time. 10 hrs last yr, 5 this year so far. Machine ran great until last week. Here is the Parts PDF Page 3 shows the exploded diagram, this engine has the Auto Choke.

The problem: Gas leaking out of carb while engine is not running. Gas trickling from ports on either side of the Valve Choke (#108).

What I've done so far: Removed air filter, float bowl, carb float, valve needle and seat. Checked for obstructions, none but cleaned it anyway. Replaced all parts. Reattached gas line. Once the float bowl fills up, gas continues to pour out of the two ports. When I first disassembled, the needle seat pretty much fell out. When I reassembled, I pushed it up as far as it could go. Wondering if I pushed it up too far, I installed the needle and the carb float. Leaving the float bowl off, I reattached the gas line. Without applying upward pressure to the carb bowl, gas flows down the needle, as it should.

When I apply light upward pressure on the carb float, I can feel the needle seat itself up against the seat, when that happens the gas stops flowing. So I assume its working ok. I reassemble everything and start the mower. After priming itself, it chugs to a start then works ok. Ran for about 1 min. No leaks. I leave the mower and come back 30 minutes later and gas is again pouring out of the carb, from the two ports on either side of the Value Choke. Definitely out of the port on the left, and seemingly out of the right port too.

Question: What could be the problem? I don't know much about small engines other than knowing the problem has to be air, gas or spark. It gets air, fresh gas and a new spark plug was bought to eliminate that issue.

Thanks for your help in advance.


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canguy(British Columbia)

There is a replaceable Viton seat at the bottom of the bore that needs replacing, p/n 631021B. You can remove the old one with a small pick or a shot from an air nozzle into the fuel line barb. Make sure you aim it away from anyone if using the latter method.

    Bookmark   August 17, 2008 at 1:03PM
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Thanks. From what I can see, that needle seat looks ok. Not cracked, or chaffed. If need be, where can I order that part?

    Bookmark   August 17, 2008 at 4:01PM
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Sometimes, when you remove the fuel line, you'll dislodge some crud.
Upon reassembly, this crud gets washed down into the needle/seat, causing it to leak again.
I'd clamp off the fuel line-
Remove float & needle-
Unclamp fuel line and let it "flush" a few seconds, reclamp-
Reinstall carb parts-
Upon successful solution, it'd probably be a good idea to change the oil, since some gas has probably seeped into the crank case.

    Bookmark   August 17, 2008 at 4:45PM
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Hi Bill,

I tried your suggestion. Put it all back together and started up the mower, ran for 30 secs, stopped it. Then sat back to stare at the carb to see if it would leak. Waited a few minutes, no leak. Thinking that "maybe" I was successful, I pushed the mower across the driveway (crushed stone) to the storage shed. By the time I got to the storage shed, teh carb was leaking gas.

Back to square one. :(


    Bookmark   August 17, 2008 at 7:10PM
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Replace your needle and seat.Take a close look at the viton seat one side has a groove and it goes down in the carb,and the smooth side goes up where the needle seats on.The part # above is the number for a tecumseh.If you have a briggs engine the part #is 398188.Hope this helps.


    Bookmark   August 19, 2008 at 4:23PM
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Hi Jerry,

Thanks for that.Yes it is a briggs motor, 6.75hp. You're the first one to mention the viton seat having a groove. Everybody else I spoke with (outside this forum) thought the grooves were the problem. The needle and seat look brand new, no build up, no corrison, no cracks upon closer inspection with magnifying glass. Yesterday I had a devil of a time getting it to continue running. When I could get it started, I'd have to remove the entire air filter apparatus. Once it ran, I could put everything back on. As soon as I started walking down a slope on the lawn (+30 deg) the engine died. Took it all apart again and discovered the seat had turned partial around in its position so it wasn't sealing at all. Straightened that out and tried again. This time the mower worked ok. My frustration level was quite high at that time. I was ready to let it roll down the hill into the forest below. =8-#



    Bookmark   August 19, 2008 at 6:01PM
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Glad you got it going,this forum,has help me a lot too.


    Bookmark   August 19, 2008 at 6:27PM
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Hi there people I have a Ryobi taipan 31cc lawn trimmer. It,s about 11 years old and it has never given me any trouble. Recently I rebuilt the carby and now when I prime it fuel starts leaking heavily out the air intake
Can Anyone tell me what the problem is?
Thanks for any feedback. Much appreciated

    Bookmark   January 21, 2013 at 4:56AM
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IMO or guess probably the same problem the needle not seating on the seat shutting off the gas. when you push the primer buttom it just pushes it pass the needle and seat. If I remember how this works???? when you start the engine after priming (pushing the primer buttom it just circulates gas up and through the carb. but not pass the needle and seat). once the engine starts or enough vacuum pulls the needle off the seat so gas will flow??? I think?? other may give a better or more accuate opinion??

    Bookmark   January 21, 2013 at 12:02PM
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Try floating the float in about 3 inches of gasoline, in a clean coffee can. Overnight. Might just have a leaking float. RJ

    Bookmark   January 21, 2013 at 7:31PM
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Hey people I dismantled the carb again cleaned again and the fuel keeps coming out of the air intake. I played around with the thing a ma bob that controls the rubber tipped pin which regulates the fuel. Still the same. I know I'm close to getting it going but frustration is creeping into my game. S.O.S

    Bookmark   January 22, 2013 at 4:48AM
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jimbo you probably need to post over in the toolshed forum for trimmers. most won't respond when highjacked on another post on different forum...if that's the craftsman model thats got the spark plug on the bottom good luck.

    Bookmark   January 23, 2013 at 7:43PM
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