300 Farmall float adjustment, long post (2024)

My needle valve had been sticking shut so I purchased a new needle, seat, & bowl gasket from my IH dealer. After installing the new needle & seat,no more sticking, the tractor ran very rich with more black exhaust than normal. I removed the bowl & it was nearly full of gas. My I&T book doesn't show a spec but the bottom toe of the float to the base of the top half of the carburetor measured 1 1/8". I changed it to 1 3/8" & got some improvement. I also measured both needles & found the new one is slightly shorter .025" than the old one. Does anyone know what the actual gas level should be in relation to top of the bowl? Sorry for the long post & thanks in advance. Sonny

That is why there are adjustment screws!
With the engine warm & running wide open, turn the high speed screw in until the engine slows (lean) then turn out until it begins to "blubber" & smoke (rich). Reset the screw 1/2 way in between and then turn out about 1/2 turn for power.
Idle the engine & repeat for the idle AIR screw; turn in for rich and out for lean. Set 1/2 way in between.
Adjust idle RPM's & repeat the sequence for quality control.

The Super H-up carbs are not adjusted like the H. Provided someone has not put the wrong parts in them, 5 turns out is max power, it can be turned in for lighter loads, or if it appears to be too rich. It is not to be turned in until rough, etc.

I suspect the new needle is either wrong or at least different. It came in a package with a big part # C5AV & a host of additional numbers, don't know if it's IH or not. The gasket came in a different bag & was marked CNH. I never thought to measure the new one before I installed it. It did solve my needle sticking problem so I thought that if I could find the correct gas level, I would adjust accordingly & call it good. Thanks.

I just found a # on Case IHparts.com saying my part should be 47396DAX40 & that number is on my parts bag so I have the correct part.

Rusty, Nope -- If you will check the M/Super M carbs closely you will find the the discharge tube on the SM has smaller holes than the one for the M. The jets are the same, the part numbers of the discharge tubes are different. The smaller holes allow less flow at a given setting, allowing the main jet screw to be screwed out farther. I have not seen this explanation in print and I don't know what else is different, if anything. I will stand corrected if what I have said is incorrect. However the SM I am working on how came with an M carb. I got a SM carb from Mike at Steel Wheel Ranch and that is when I discovered the difference in the two carbs and the reason why IH changed the adjustment given in the operators manual. On my Super H, when I bought it several years ago, I adjusted the carburater the old way, went up a slight incline, and it almost died. I then read the operators manual, and found the 5 turns out thing. You are right when you say that the final adjustment will be when the tractor is put to work, but the adjustment on the Super H and Super M-up will have more turns than on the non-super H and M.

Rebuilding has nothing to do with adjusting. The directions in the Operators manuals differ between the H/Super H, and M/Super M. It is in the manuals in black and white. Perhaps you don't have the Super manuals, I see no other reason for you to disagree. If you use the 3 turns out for the initial setting the H and M will probably run ok, but the guy getting your carbs should adjust with the in until rough out until smooth to assure a lean mixture. The Super H/M-up will not run properly if adjusted that way, at least not with any load. I have a 460 that I tried with 4 turns out, it lost power so I use 5 turns. It runs a little rich possibly due to some other problem, but more likely because it doesn't get run enough.