140 carb problem

This one has me baffled...

Got the Bendix carb off a friend's recently purchased 140. He brought it to me complaining the carb slowly drips gas from the weep hole in the air inlet when shut down.

When I opened the carb I found it absolutely pristine inside - not a trace of varnish, dirt, etc. It appeared to have a new float needle/seat assembly. However I installed a new needle/seat and bowl gasket, checked the floats for binding/leaks (there were none), checked the float level (it was in spec) and put it back together.

When installed back on the tractor, the engine started and ran perfectly. However a few minutes after shutdown it started the slow drip again, just like before.

I set the float level 1/8" lower but found the bowl would not fill so the tractor could not be started. Bringing the level up 1/16" got it to fill again, but once again the drip returned.

I've swapped back the old needle/seat; it still either leaks or won't flow gas depending on the float level adjustment.

When it does drip gas, it overflows out tip of the main nozzle beneath the throttle plate. Fuel is NOT leaking from a bad nozzle gasket, a crack in the bowl casting, etc

Any thoughts to what the problem might be are appreciated!

Are the float needles rubber tipped ones?? If yes they have not set in to the needle so you have the set them by opening up the carb and drop the needle is the seat and lightly tap on it a couple times with a punch or other such thing. After doing that if you look you should see a little ring on the tip where it has a set in it

How about the needle seat gasket? Is it there or maybe damaged.

Needle can't fully shut off the flow. Gas level in bowl rises above the top of the main jet outlet level and floods air inlet. Either that or there is a crack between the carb inlet fitting and the needle seat threads in the upper half of carb. I suppose that could be tested with 5 lbs of air and your thumb over the brass needle seat.

If the symptoms are the same with either the new needle and seat or the old one, and the float height is within specs, I would suspect the carburetor is cracked somewhere.

Agree with what others have said - but still think it's a much better idea to always turn the tractor off by turning the gas off and running the carb dry.

Especially if it's not in daily use.

Then this problem is sort of a moot point.

Not suggesting you shouldn't fix it of course.

Hmm...is the gasket under the seat? (I know this is basic but thought I would ask)

If the float was adjusted low, it should still drip gas if leaking thru the seat threads. (provided it is given enough time to refill the bowl to over flowing)

just because the needle and seat are new, that is not to say it is seating properly. When I install a needle and seat, I hold the carb upside down and blow on the fuel inlet to see if it leaks or not. Sometimes it takes trying more than one or 2 needles and seats before you get a tight fit.
My 100 drips gas from the carb when sitting for a while, has for 40 yrs, I just shut off the gas at the sediment bowl when I shut the tractor off, and turn it on again when I want to use it. Figured that is wasn't worth the time to try and fix it.

Even if it has a viton tipped needle,I usually form the seat by coining with a tool I have. I find very few new needle and seats that are true. I don't blow in the inlet, I suck and if it will hold the tip of my tongue for a period of time I say it is good to go.

Thanks all for your suggestions! Looks like coining of the viton tip will be my next step (was unaware this was safe to perform on a soft-tipped needle).

Will share back whether this solves the problem!

Bob M

(quoted from post at 13:05:07 01/03/12) Thanks all for your suggestions! Looks like coining of the viton tip will be my next step (was unaware this was safe to perform on a soft-tipped needle).

Will share back whether this solves the problem!

Bob M

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Bob, I have never done such a thing as "coining" or tapping on a needle to seat it. The only thing I do that is not suggested in any repair manual is to spray both the needle and seat liberally with aerosol carb cleaner, blow them dry, and then MAYBE a quick shot of silicon lube on both just to prevent sticking on the initial start up.

The Viton tipped needles were developed to get a longer life from the needle and seat. The old, all steel needles would wear a groove where they contacted the seat, and naturally then they would leak. Tapping on the needle to seat it CREATES a wear groove, which is exactly what you do NOT want.

I will ad one more test. With the bowl off, and the float and needle in place, hold the float up gently, and turn on the fuel. With a Good LED light, finding the source should be a piece of cake. One issue not mentioned is that the tang of the float that touches the needle must be flat to the needle. Best of luck, Jim

Thanks Jim!

I tried your test earlier and found the needle does not leak when the float is manually held up. But checking the float tang for perpendicularity to the needle button is an excellent suggestion - will check that next.

Bob

This trick may help in locating the leak.
HTH, Hendrik
Replace lower half by glass bowl...

I have never worked on a Bendix carb for a tractor. Zenith, Marvel Schebler and and the IH for cubs, yes. On the IH Cub unit, the discharge nozzle screws in the lower carb body at a point that is below the fuel level in the bowl. If the gasket leaks on the nozzle, fuel will leak out even if the float needle seals perfectly. The discharge nozzle projects upward to end in the center of the venturi. I coat that gasket with #2 Permatex a day in advance if possible before assembling it.

(quoted from post at 11:15:16 01/05/12) I have never worked on a Bendix carb for a tractor. Zenith, Marvel Schebler and and the IH for cubs, yes. On the IH Cub unit, the discharge nozzle screws in the lower carb body at a point that is below the fuel level in the bowl. If the gasket leaks on the nozzle, fuel will leak out even if the float needle seals perfectly. The discharge nozzle projects upward to end in the center of the venturi. I coat that gasket with #2 Permatex a day in advance if possible before assembling it.

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Bendix/Zenith. Some of the Zeniths also had the Bendix name on them.