Hello to all:

I found this forum while searching for an answer to my lawn mower conundrum:

My landlandy's Craftsman lawnmower appears to be leaking gas out the carburetor; I assume this because gas is leaking out the primer bulb, and the air filter gets soaked with gas when I try to fill it up. The mower will not start, period.

I have searched on the Web and found much discussion about this kind of (seemingly common) problem. Here are the vital stats on my mower:

Craftsman model: 917.378361
Briggs & Stratton engine model: 123K00 series

The answers I have read on the web involve replacing/removing and cleaning the carburetor. This model mower DOES have the brass nut on the bottom of the carb. Can I replace just the bottom of the carb as I have read in posts about the Techumseh engine, or do I need to replace the ENTIRE Briggs/Strat carb? Thanks in advance for any help!

your going to have to take it apart and replace the Needle & Seat

its possible that theres some dirt thats stopping the needle from closing properly, but if your going to take the carb apart, you might as well replace it anyways just to be safe.

Pyro's right, replace the needle and seat, which is the common cause of carb flooding or overflowing. Removing the top shroud will make carb easier to access/remove. 3 bolts hold air filter base on, 2 on carb, 1 on support bracket. 2 bolts hold carb on, have to twist carb to remove governor/throttle link.
you can rebuild carb using Briggs # 498260 kit, current Briggs retail is $7.25. Disassemble and thoroughly clean carb, best to put in carb dip for an hour or so, but a can of good carb spray cleaner will usually work, I use Wal-Mart supertech blue can. Spray out all passages in carb, especially ones in carb throat by throttle plate, and the bowl nut. need to blow out with compressed air. if air filter was good, air drying might get you by, but a new one is less than $5. Be sure to drain/replace oi, 20 ounces of 30W.
hope this helps,
thanks,

Thanks so very much for the replies...I'm looking at the carburetor, and my next question is, once I've removed it from the lawnmower, and taken the bottom bowl/float off, does the actual metal housing of the carb split in two at all? I'm looking inside at all these small parts (the red rubber needle seat, etc) and at first glance it looks very difficult to get that little red rubber seal in and out. Am I missing something here? Or should I just soak the entire assembly in carb cleaner immediately after taking it off the engine block?

Nope, doesn't split in two. Sometimes the seat will blow out if you use compressed air at the fuel inlet. I've gotten out several ways, once used a drill bit a little larger than the hole in the seat, turned it in with fingers to grasp seat and pulled it out, also made a hook from stiff wire bent at right angle then snipped off all but about 1/32", pushed thru seat hole and pulled it out, being careful not to scratch chamber it sits in.

ya, a straight pick is the next easiest way to get them out without compressed air

Wow, you guys ROCK...one more issue: is the plastic float (kinda looks like a miniature toilet seat) supposed to be filled with fluid? Mine is...I can't tell what's inside; I've tried putting the float in a cup of water, and it does indeed float. There are no pinholes that I can see, so I can't imagine how any gas could have gotten inside it.

The float should not have any fluid in it. The float works like a toilet float. When the gas in the bowl is used by the motor, the float goes down just like when you flush a toilet. This allows the needle valve to be unseated and the gas to fill the bowl. When the bowl is full the needle valve is pushed back up into the seat by the float which stops it from overflowing and eventually leaking out of the carb.

The float should not have any fluid in it. The float works like a toilet float. When the gas in the bowl is used by the motor, the float goes down just like when you flush a toilet. This allows the needle valve to be unseated and the gas to fill the bowl. When the bowl is full the needle valve is pushed back up into the seat by the float which stops it from overflowing and eventually leaking out of the carb.

Excellent description Slugger.
I think I'll cut this to paste in future threads....
In all my born days, and believe me that's a lot, never seen a plastic float get filled with gas, maybe 30year has ??

Yes, I have seen a few with fuel in them, but not many. Most plastic floats are seamed together, I would think the seam has a leak that allowed the fuel to enter, but thats just my guess.

The reason that it will float in a cup of water, is that gas is lighter then water and gas will float on water. A float assembly filled with gas will still float in a cup of water, but not in a cup of gas.