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M Carb Dumb Question Time II

D

Dan Bear Kelley

Member
Help time! I got my M back together yesterday. New plate on the water jacket. Rebuilt the carb. Hit the starter and filled the barn with blackish smoke. Not oil-burning smoke. Way too rich carb black smoke. Closed the idle screw all the way, and she kept running. Closed down the power screw most of the way and she kept running. I finally had to shut her down and get some fresh air. After she aired out, I tried again, and she was mostly flooded.

I was VERY careful in the carb rebuild. New needle and seat. Correct gaskets. Clean clean clean. Double checked the float height three times. Possibly an air bleed is blocked? or the float has sunk?

I have a couple options. I can rebuild again, this time replacing the float. OR I can get a rebuilt carb.

I am leaning toward getting a rebuilt carb, as it is obvious that this one has been rebuilt a few times. I could be trying to fix unknown problems caused by someone else's inventiveness.

The problem is that there was no tag on this carb. So, I do not know what model it is. There are (at least) two carbs for the M. My M was built in 1951, if that is any help. So, if there was an early model carb and a later model carb, mine is more likely the later model. Can anyone point me in the right direction of which carb to get?

One final thing. There is a persistent gas leak out the bottom of the carb where there appears to be a round plug of some kind. This is not the drain, which is a small square-headed pipe plug. This is dead middle of the bottom. Anyone have any ideas on stopping this leak?
 
The "leak" on the bottom you don't want to plug. That is where the excess fuel leaks out when it floods, it has a felt or some sort of fiber in it to allow fuel to leak out but keep dirt out. Float could be hanging up inside, it runs pretty close to the inner castings. Could also be a bad float, you can drop the bottom of the carb off and remove float without taking the whole thing off. Did you get the shaft from the governor to carb in the right place when you put it back on? The end goes in a notch in the throttle linkage inside the carb. I have noticed a difference in carb kits also, got one that had the wrong needle and seat.
 
No need to worry about which carb you have. Both models can be rebuilt to the specs for the gasoline only model. If you need a rebuilt carb, just give me a shout. I"ve got two that are ready to go.
 
Whenever I put an M style carb together, I like to shake it around a bit to make sure the float moves freely. I've seen gaskets catch the float and I've had to bend the float a bit to make sure it clears the bowl.

Chris B.
 
I just had the same problem with my super H (it has an M carb). I found 2 problems:

The pin the float pivots on was too small and too tight and it would not let the float close all the way with floating pressure. (it would close when I pushed it)

The float was also hitting the inside or outside of the bowl in the carb and was getting stuck.

Fixed these two things and no problems.
 
Dan:
You probably don't need a new carb; these carbs can be rebuilt many, many times. Check to see if the float is hanging. Also, sink the float in a bucket of water with some sort of weight (being careful not to damage it). Then, release it after an hour and see if it bobs to the surface and is free of liquid inside.
Rusty does not agree with me on this - and I have a high regard for him - but, I have found in some instances of acute flooding, the "cure" is to set the float level measurement a little bigger than the spec. measurement, i.e., a little more than 1 5/16", but not even a full 1/8" more. Maybe 1/16" or 3/32" more. This will lower the fuel level in the bowl and help prevent flooding.
mike
 
I have found that when a carb is rebuilt and put back on the tractor there is a good possibility that a tiny particle of "stuff" may get in the needle & cause it to leak at first.
What I recommend is:
1. install all parts except the fuel line.
2. open the tank shutoff and catch a cupfull of gas. shut off the valve.
3. attach the fuel line.
4. remove the small drain plug (square end) and allow some fuel to drain out by opening the tank valve again. With the float hanging down, any small particles of "stuff" will flush through the wide open needle valve.
5. replace the drain plug & all should be well.
 

Daniel, there are only two reasons to purchase a rebuilt carburetor:

1. The original carburetor is missing.
2. The original carburetor is physically broken. That is, it looks like someone beat it with a hammer, not some invisible "maybe" thing.

Anything other than that, and buying a rebuilt carb is a "sucker" purchase.

All the "wear" parts are replaced in the rebuild kit.

You can be very careful and clean, yet still screw up the rebuild. Don't be discouraged, it never goes right the first time. For anyone.

It sounds like the needle isn't closing. That could be due to the float catching on the side of the bowl. There isn't much clearance there. Also check for a pinhole in the float. It fills with gas and sinks.

Had the same thing happen to mine. All you can do is take it apart again, recheck everything, and put it back together again.
 
Does it have a good flow of gasoline to the carburetor? Since you said before that the manifold was loose, did you replace the gaskets? Are the carb to manifold bolts tight? Both carbs will work.
safety2.gif
 
Just trying to help
1st- I know dumb but your choke wasn't pulled was it.
2nd- turning the idle screw all the way in reduces air to the idle circuit and actually richens the mixture. Screw idle jet out to lean mixture
3rd- turning load screw in leans the load circuit and I believe will eventually cut off fuel to the idle circuit if turned all the way in.
 
I have had this same problem as well. What i found was that the float was catching on the inside of the carb. I first took a dremmel tool and smoothed the area where the float what catching. (The inside of the carb has a cast surface which is very rough.) Then adjusted (bent) the float into place with a needle nose. BE CAREFUL on this step tho, it is very easy to bend, but most likely will need to be adjusted. Hope this helps. Good Luck!
 
LOVE the cartoon!

I do have good fuel flow. New fuel line and new screen/sediment filter gizmo under the tank.

I did not put new gaskets in the manifold. It's on the list, though, since I found it loose.<rb>
Carb is nice and tight to the manifold with a new gasket.
 
I [b:654c4848f0]***[u:654c4848f0]LIKE[/u:654c4848f0]***[/b:654c4848f0] this procedure! GOOD THINKING here! Aircraft folk always drain a little off the bottom. It gets the water out.
 
I just want to mention that I have several carburetors that were totally rebuildable before an inexperienced tinkerer worked their magic on them. Those carburetors still have some value as parts donors, but basically are worth no more than what they weigh for scrap iron. Farmall H and M carburetors are no longer being built. You cannot buy a new one. Those carburetors that still exist are all that we have. If you are going to do your own carb rebuilding, please be careful. Do not force anything to come apart, and please, do not make any modifications that are permanent. These old carburetors are worth anywhere from $50 to $100 as a rebuildable core, but only if nothing is broken or otherwise damaged.
 
Howdy
I think everything was covered to solve your problem but I have to add------when rebuilding a carb, everything should be hospital clean. A particle of dirt or rust that can hardly be seen with the naked eye can cause the problem you are having. Tell your wife that you need the kitchen table for an hour and do your carb there. Do not however ask for the table if you want to rebuild your M engine.
Bob S.
 
This is a great tip! I actually have a special desk in the garage, just for doing delicate work like this. I wiped it down with a Clorox wipe before I started with the rebuild. :)
 
Thank you! And thank you, too, for sending your contact information off-line, in case I give up on this. I'm actually quite encouraged by the advice I've received here.
 
There are also a few places where dirt and crud can hide that are not visible to the naked eye, so unless the carb is totally dismantled before putting it in the carb cleaner, you could have some frustrations.
 
Just a thought. First M carb I rebuilt, the piece that holds the float pin, has a hole in it with a slit so it can be made tighter. IN other words the pin just slides in the holes and is held in there by the tension of the piece it slides through. I probably not describing this very well, but my tractor flooded just like yours is. When I took the carb apart the pin had slid halfway out and the float was rubbing on the bowl. Longwinded but could be. Bernie Steffen
 
That is exactly what happened to my neighbors M.. He had a guy rebuild the carb, but he failed to ensure the pin was tight that the float was pinned too. It went off to the side, the float cocked, and it wouldn"t shut off the needle valve.
 
When I rebuilt my carburetor the first time for my H it would barely run.It was flooding like that and black smoke.It was the float was hitting the inside of the carburetor sticking it.Also when I rebuilt it the second time I left it in the cleaner overnight and it was a lot cleaner that time.I even found a passage or 2 I didnt see the first time.Blow it out with compressed air before you put it together.If there is an opening you can blow air into,air has to come out somewhere or its is still plugged and maybe needs to soak longer.Not having rebuilt a carburetor like that before,when I soaked it the first time it looked clean when I took it out of the cleaner,but it wasnt.Just because all the grease and dirt is off of it doesnt mean its really clean inside as it should be.There are little holes that are hard to see even if its clean and if you didnt know they were there,you could miss them real easy.Air in,air out,and it should work if the floats not sticking.You might need to bend the tab carefully just a little to one side or the other,like it might be twisted a little,and it doesnt take much.
 
Dan Bear. I like the way you reply to every post. Some people never reply so you don"t know if you did them any good or not Bernie Steffen
 
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