M with a flooding carb

Farmall M, Super M, 400, 450 & 560 Tractors, 1939-1963

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Radec Aksarben
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M with a flooding carb

Postby Radec Aksarben » Thu Jun 04, 2015 10:41 am

I always leave my gas on at the tank when I shut down my M. Over the winter it would flood the carburetor when I tried to start it. It would not start and just kept flooding. So I rebuilt the carburetor.

When I put the carb back on, I turned the gas on at the tank and it just started pouring out of the carb as fast as it would run through the line.

I unhappily shut the gas back off, removed the bowl of the carb to inspect the float operation. I used my hand to move the float up and down. The needle valve shuts the needle off when I moved the float by hand.

I took the float off and verified that it floats. I carefully adjusted the float height so it should be correct.

I put it back together and same thing. Gas pours out of the carb.

Here is what I really don't understand:

I had to get mowing done so I let the gas stop running out of the carb. I started the tractor and then turned the gas on. It ran fine. I then proceeded to mow for 3 hours at different engine speeds with the M and it ran beautifully. It worked great at idle and driving down the road up big hills. When I was done, I turned the tractor off and waited. Gas started pouring out of the carburetor.

What the heck?

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Re: M with a flooding carb

Postby Scrivet » Thu Jun 04, 2015 8:39 pm

Float or pivot hanging on something. Vibration of engine running shakes/keeps it loose.

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Don McCombs
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Re: M with a flooding carb

Postby Don McCombs » Thu Jun 04, 2015 10:01 pm

Radec Aksarben wrote:So I rebuilt the carburetor.

What did the "rebuild" consist of?
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Radec Aksarben
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Re: M with a flooding carb

Postby Radec Aksarben » Fri Jun 05, 2015 11:27 am

Don McCombs wrote:
Radec Aksarben wrote:So I rebuilt the carburetor.

What did the "rebuild" consist of?


I took it apart, soaked it in cleaner, rinsed it, put it back together with new gaskets, main needle screw packing, needle valve assembly, float pivot pin, idle screw... etc. I can't think of any other new parts off the top of my head. I put a different screen assembly in, though not new, because the threads were bad on the old one.

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Re: M with a flooding carb

Postby Don McCombs » Fri Jun 05, 2015 6:37 pm

I'm not very familiar with M carbs, but by "needle valve assembly" I'm assuming you mean the float needle valve. Did you use any type of thread sealant on the needle cage where it screws into the casting?
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Radec Aksarben
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Re: M with a flooding carb

Postby Radec Aksarben » Mon Jun 08, 2015 9:48 am

Yeah, the float needle valve. I did not use any sealant on the threads.

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Re: M with a flooding carb

Postby Eugene » Mon Jun 08, 2015 10:57 am

You shouldn't need a sealant on the needle valve seat threads. There is suppose to be a gasket under the seat.

Where did you purchase the carburetor kit?

I purchased a carb kit. The needle valve seat in the kit was longer than the original seat. I located the original needle valve and seat. Lapped the needle valve into the seat. Problem solved.
I have an excuse. CRS.

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Radec Aksarben
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Re: M with a flooding carb

Postby Radec Aksarben » Mon Jun 08, 2015 2:03 pm

It was some random Ebay store that had sold dozens of them.

I compared the needles before I installed the new one and they looked the same. I mentioned earlier that when I took the bowl off the carb with it still on the tractor and fuel still hooked up, the needle valve operated properly when I moved the float with my hand. The float drop and upper position still looked good.

It seems like maybe Scrivet is on to something. I wonder if running it long enough will "loosen" things up or if I will have to take it apart again and try to adjust the float again to be certain it clears the housing.

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Don McCombs
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Re: M with a flooding carb

Postby Don McCombs » Mon Jun 08, 2015 3:12 pm

Eugene wrote:You shouldn't need a sealant on the needle valve seat threads.

I have found otherwise. Especially if the area between the casting and the gasket is corroded.
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Re: M with a flooding carb

Postby Scrivet » Mon Jun 08, 2015 10:42 pm

Radec Aksarben wrote:...........It seems like maybe Scrivet is on to something. I wonder if running it long enough will "loosen" things up or if I will have to take it apart again and try to adjust the float again to be certain it clears the housing.
It'll never fix itself, go ahead and take the carb apart again. :( Look for the float rubbing on housing, float rubbing on gasket inside, pivot pin to tight in float so it doesn't swivel up and down easy, pivot pin bent oh so slightly so the float doesn't swivel easy, float "axle hole" bent/oval, float Y shape bent to far apart or to close together, etc.

Somewhere, something isn't just quite right. Turn on all the lights up high and get out the magnifying glass. Gas doesn't exert much force pushing up on the float, it doesn't take much resistance to keep it from moving.

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Re: M with a flooding carb

Postby p5388 » Tue Jun 09, 2015 10:29 pm

Have you checked the float to make sure it hasn't been invaded with gasoline? (ie. shake it and see if it "sloshes")
Even if the float height is carefully adjusted to specified height, a change in it's buoyancy will keep it from shutting the float needle...

Another way I use to test float height is to connect the carb body to an alternate fuel source (my "test tank"), with the bowl off, and slowly rotate the carb body upside down until the weight of the float stops the fuel from flowing... saves a whole bunch of putting together, installing, removing, etc...

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Re: M with a flooding carb

Postby Matt Kirsch » Thu Jul 02, 2015 7:30 am

While it's been almost a month, +1 on "take the carb apart and try again." Hopefully you've already done that.

You're not the only one. I had to take my Super H carb apart SIX times before I got it right. On mine it would jam the needle closed.

Those M carbs are a pain because you can't see if the float is hitting the bowl, and you only have to be off a fraction for the float to hit the bowl.

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Radec Aksarben
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Re: M with a flooding carb

Postby Radec Aksarben » Wed Jul 29, 2015 4:19 pm

Well, since I never have much time to fix/play, I just kept turning off the fuel when I shut the tractor off and cracked it open before starting the tractor. Once the tractor started, I would open the fuel valve the rest of the way. I did this for all subsequent use, including about 200 miles of driving it in a tractor drive (Boy it ran like a champ! :{_}: ). It doesn't flood anymore... but I still am shutting the fuel off after using. :D

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Re: M with a flooding carb

Postby Matt Kirsch » Thu Jul 30, 2015 12:41 pm

That's not a bad thing to do, regardless.

Does gas still pour out? Your float needle isn't sealing for some reason or other.

I have a Super H which has the same style carburetor with the split float that goes around the venturi. Clearance is VERY tight; you only have to be off a mere fraction for the float to hang on the side of the carb bowl. Mine would hang and hold the needle closed, so the tractor would run out of gas in 30 seconds. Dad and I took mine apart several times before we figured out where it was hanging.

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Radec Aksarben
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Tractors Owned: '48 Farmall Cub w/ IH-Danco C2 belly mower
'49 Farmall M w/ factory disk brakes (not super style)
'51 International I-9 - rusty yellow
Circle of Safety: Y

Re: M with a flooding carb

Postby Radec Aksarben » Thu Jul 30, 2015 4:20 pm

No, gas doesn't pour out anymore. I forgot to turn the gas off a couple of times when I parked it for maybe 10-20 minutes and there was no puddle. When I first started this thread the pouring would start after maybe 5-10 seconds.


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