Super M carb adjustment(double checking here!!! :(

mike1972chev

Well-known Member
I know this has been asked thousands of times,but I want to make sure on this .(I am NO WHERE near my manual right now.)

In my photo #1 is the idle,#2 is idle air adjustment,and #3 is high speed mixture adjustment. Is this correct????

I can adjust #1 and #2,but CANNOT get #3 to do anything at all !!!!! I have the throttle wide open when adjusting it and it is doing ZERO to change the running quality of the engine.

Should I be looking for a plugged passage somewhere internally????
a123532.jpg
 
Set #3 at 3 full turns out and leave it there. You ABSOLUTELY will not notice any difference in how the tractor runs UNLESS the engine is wide open under FULL load. If the engine sputters and stumbles under full load, then open the #3 screw in 1/2 turn increments until it smooths out. If the tractor is doing ONLY light work, such as tractor rides or parade duty, then the #3 screw can probably be turned IN to 1 1/2 to 2 turns out for better fuel efficiency.

Try to understand the "load adjustment" screw. It provides a way to adjust the amount of fuel the engine receives in order to realize the greatest fuel effiency under varying WORK LOADS.

The factory initial setting IS 3 turns out.

For what it's worth, that carburetor in the picture is for an M. It is NOT a Super M carburetor, but will work equally well. A Super M carburetor will have the choke lever on the INSIDE.
 
RustyFarmall's advice is right on. However you can make a fairly close adjustment to the load screw like this:

With the engine fully warmed up and running at SLOW idle, quickly pull the throttle wide open. If the engine stumbles or stalls, open the load screw 1/2 turn and repeat. Continue until the engine accelerates without any stumble.

You may see a hint of black in the exhaust when you as you snap open the throttle - this is OK. However if there is any black in the exhaust AFTER the engine reaches governed RPM, the load screw is set too rich - turn it slowly back in just until the black disappears.
 
Thanks Rusty,

BTW,I just "stole" that picture from EBAY to use as an example to draw on . My Super does have the choke set the exact opposite from this picture and is on the INSIDE/block side of the carb.
 
I gave a long explanation of the SM vs M carb, D Slater showed what the operators manual said about the SM carb as I was typing. After posting I agree with Rusty that that is a M carb, not a SM, so I deleted my original post. My 460 runs better with any kind of load, leaving the adjustment 5 turns out. Perhaps it could be turned in for part throttle light loads such as cultivating, I have never tried that.
 
You say the load screw does absolutely nothing. Do you mean you can screw it all the way in and it will not kill engine or keep screwing it out and notice no change. A lot of the packings behind nut are too long and needle will bottom in nut before end of needle gets to the main jet inside carb. Another thing, there are different lengths needles used with a different taper on needle and jet also for power improvement packages like fire craters. Then the main jet is calibrated for full load so screwing it out ten turns will not give more fuel than the size of jet, only limit amount delivered for light loads. On a side note, first 450 gas I did a valve job on had a burned intake valve with low hours from needle screwed in to save that extra fuel but he used it that way on all loads. IH did give him a free valve job though.
 
I ran it all the way in (gently)and it did not shut any fuel off. ALL the way out made no difference either.

Also,I am about 99% + sure this is the original carb that came with it. (Date codes match for 1953)

I will check your suggestion on that packing being TOO thick. It never felt like the needle EVER bottomed out against a seat.
 
Yes, the needle on my 460 carb never gets inside the jet. The carb on my Super H can be adjusted just like the H carb-turn in until rough, out until smooth-I did that after cleaning the carb and found that it had power to move the tractor, but that was all. I then read the Operators manual and found that max power was 5 turns out. I haven't driven the SH with much of a load. I have experimented with the 460 and a bush hog, it runs better 5 turns out, maybe 4 if I never leave 2nd. 3rd is a little fast for mowing so I use 4th TA, faster than 2nd, slower than 3rd. I guess the answer is don't mix parts even though the carbs look the same.
 
If you look in the parts manual you will see a different adjusting screw and main jet for fire crater pistons. It has a different taper, length and the main jet it larger but I can't remember if it is longer or shorter than original. It is also calibrated for full load horsepower at five turns out so it is way clear of the jet for zero restriction. Actually most are clear at about 3 l/2 turns out after bottoming. Can't tell by looking at carb what parts are inside of them even though there was no updating of the number on the carburetor.
 
You won't see or hear any change in the rpm of the engine when changing the load screw at idle . It is not an idle jet. As others said you have to apply the throttle or go work it to adjust that. Hook up your plow or cultivator and make some adjustments. If you don't see changes there the carb is *********
 
All fuel must go through the main jet on a m carburetor. If it is working and put together the way it is supposed to be you can kill the engine at all speeds, low idle , high idle or any where in between. Some seem to think that the fuel for low idle comes from a different source. It has it's own jet but still that jet is supplied from main jet. What I am saying is a ton of these carburetors the main adjusting screw does not contact the main jet. As a preliminary adjustment I warm engine, run at high idle and screw it in until it starts to stall, or miss, or slow down or just change tunes. Then back it out a half turn or so and see how it performs and go from there. If it has an oversized main jet or someone has been in there with a drill things will be different and you may even get a bunch of black smoke when you turn it out that extra half turn or not be able to kill it when you screw it in. Best way to see if it will kill is with it apart and screw it in while watching the needle enter the main jet and then blow air through the nozzle.
 
Pete maybe this will help your memory. Load screw on the right is a regular M. Other stuff is the change over kit for a M? Did some use them in a SM carburetor. Didn't know IH made a changeover for a SM carb?
a123674.jpg
 
Pretty hard to refresh this old memory. I don't really remember if we changed jets on the supers or not. I do know we did on the M's. Easy to see the different lengths of both the screw and jets in your picture and why mixing them up can cause all these different symptoms guys come up with.
 

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