M carb float and needle valve problems

Marty from MN · Jul 6, 2012

I put a rebuild kit in my '51 M carb last year and have had nothing but trouble with it. The needle and seat were replaced, but I wish I would have kep the original ones. The new one has the rubber tip and it will not seal. Also the hinge rod for the float seems too short and will not stay in place. I have had to take the carb apart at least a dozen times to fix the float hinge and clean the needle. Put it back together and 20 minutes of run time later there is gas pooring out of the carb.

Where can I get an original style needle vavle and seat (no rubber tip)?

Is there any trick to getting the float hinge to stay in place? I've tried pinching the brackets against the rod but it still moves from side to side and falls out of the bracket. Is the hinge rod too short?

pete 23 · Jul 6, 2012

There is no problem getting the hinge pin to stay
i place. If pin is too short just make a new one
out of a nail or other suitable pin. There should
be minimum clearance between float hanger and
float, just so it does not bind. Your float may be
hanging on the sides of the bowl causing your
problem also. I took an old carb years ago, cut
the bottom out for a gauge to set those floats.
You have to determine if it is touching sides.
Many different ways of doing that. Also, the
rubber tipped needles are the best as they were
released way back in the early 60's to overcome
problems with leaking needles due to larger fuel
tanks having more pressure on needle. You have to
make sure it absolutely seals. I tip carb upside
down and suck on inlet. It has to hold a vacuum on
your tongue indefinetely. I also peen the seats
as they are often poorly made. I use a inj nozzle
needle to do so but an old steel will work fine.
Get a good needle and seat from CASEIH as their
new ones seems to be good like they were years
ago.

Marty from MN · Jul 6, 2012

It's the same float that came out of the carb, so why would it rub now when it didn't before? I'll take a look at it but I don't think that is the problem. Maybe the rubber tip will work of I can ever get the float to stay in place, I've heard of others having problems with them as well. Possibly related to poor quality though.

Brownie 450 · Jul 6, 2012

Our SC Zenith carb leaked like yours. All brass needle from IH cost $43. Solved the problem.

rustyfarmall · Jul 6, 2012

(quoted from post at 10:12:24 07/06/12)
It's the same float that came out of the carb, so why would it rub now when it didn't before? I'll take a look at it but I don't think that is the problem. Maybe the rubber tip will work of I can ever get the float to stay in place, I've heard of others having problems with them as well. Possibly related to poor quality though.

Take a good look at the float bracket. Notice how one leg is slotted and the other leg has just a hole? Have you taken the time to try and understand why that one leg is slotted?

I'll give you a hint. The slot is there so it can be squeezed together just a wee bit and make that float hinge pin fit TIGHT. The slot needs to be squeezed enough so that you need to work to get the hinge pin in place.

There is NOTHING else to keep that hinge pin in place. If it DOES NOT fit TIGHT, it WILL fall out.

Rumplestiltskin · Jul 6, 2012

Hi, Marty.

If you've replaced or repositioned the bowl gasket, the float could be hanging up on it. I always trim the inside of the gasket to match the inside of the bowl rim.

Mark W. in MI

Marty from MN · Jul 6, 2012

Rusty thanks for the reply. Notice that I mentioned that I have tries to pinch the together. Put a good crimp on it with pliers and vise grips. This was pinched right on to the part of the pin that is flat. That is why I suspect the pin is short.

Marty from MN · Jul 6, 2012

Good point Mark. I did not think about the gasket. I probably need to replace that again anyway since it is fairly beat up from taking the carb apart.

pete 23 · Jul 6, 2012

Why would it rub now ? Because it is not positioned
properly that is why. If the pin is coming out we
know something is wrong. Like Rusty said, look at
the hinge bracket. Slotted end pinches pin so it
cannot move . All of these things have to be
adjusted when you work on a carburetor. Taking it
apart a dozen times doesn't prove anything if you
don't analyze the problem and correct it.

GordoSD · Jul 6, 2012

That is why it is falling out. Make a new one the is round all the way to the end.

gene bender · Jul 6, 2012

Why dont you make a new rod for the float thats longer. Last two new needle and seat i got from the I-H dealer both had the rubber tips. How come the new ones are 21 but the gasket is only 4.35.

rustyfarmall · Jul 6, 2012

(quoted from post at 12:24:57 07/06/12)

Rusty thanks for the reply. Notice that I mentioned that I have tries to pinch the together. Put a good crimp on it with pliers and vise grips. This was pinched right on to the part of the pin that is flat. That is why I suspect the pin is short.

That pin shouldn't have any flat spots on it. There's your problem.

Also, pinch the slot together before you put the pin through the holes. You'll never get it tight enough with the pin already in there.

D Slater · Jul 6, 2012

If you can't keep the pin in, do like pete said make a longer one. Look how the bowl is made. If the pin is long enough it will hit the bowl sides before it comes out after installing the halfs together.

rustyfarmall · Jul 6, 2012

(quoted from post at 14:14:16 07/06/12) If you can't keep the pin in, do like pete said make a longer one. Look how the bowl is made. If the pin is long enough it will hit the bowl sides before it comes out after installing the halfs together.

That pin would need to be really long to make contact with the bowl sides on an M carburetor. REALLY, REALLY long.

D Slater · Jul 6, 2012

Pin sets around 3/16 inch to center back from the front bowl wall. Way the bowl is made there the pin only needs to be 1/8 to 3/16 inch longer if it has a 1-5/16 to 1-3/8 inch long pin to start with. Thats a ball park figure since some castings very some. Agree that most times the pin won't come out if the piviot frame is tight on pin at the sloted end.

rustyfarmall · Jul 7, 2012

(quoted from post at 18:45:56 07/06/12) Pin sets around 3/16 inch to center back from the front bowl wall. Way the bowl is made there the pin only needs to be 1/8 to 3/16 inch longer if it has a 1-5/16 to 1-3/8 inch long pin to start with. Thats a ball park figure since some castings very some. Agree that most times the pin won't come out if the piviot frame is tight on pin at the sloted end.

Are you sure you are not thinking of an H carb?

Ellis Kinney · Jul 7, 2012

I had a similar problem. Don't ask me how the hinge pin becomes too short, but mine began falling out on one end and the float would not function. Simple fix. A 1/8 brazing rod is exactly the size you need. add a teeny bit in length and you're back in business. Ellis

M carb float and needle valve problems

Marty from MN

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Brownie 450

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