Super M carb adjustment(double checking here!!! :( (2024)

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.

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.

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.