How to rejet a farmall carb

First, you need to identify the main load adjustment screw, the metering stem. The main load adjustment screw is located on the front of the carb bowl,, it has a textured surface and use a standard screw driver to adjust, some have t handles,,, The metering stem, sits right in the center of the carb bowl, where the venturi sits, on early carbs,,, they use a threaded brass plug on the bottom of the bowl that holds in the stem to the bowl. On 6 cyl, and later carbs, the stem screws into the carb bowl itself,,, so,, if it has a brass plug, its the old style bowl, if it has no plug its the new style bowl. OK, all the work is done simply to the carb bowl, and the metering stem,,, (or called a discharge nozzle),,,
Once the carb bowl is removed,, you then remove the main load adjustment screw and the brass nut it sets in,, dont remove the packing!! Save it if you can,, or replace it with a new one. Then, remove the metering stem from the carb bowl. Now, your off to the hardware store!! To the drill bits!! What your looking for is "Numbered drill bits" If you look in the carb bowl, where the main aduster is, you will see a tiny brass fiting sticking out,,, thats the main jet,, you need to find the drill bit, that perfectly fits your current jet size,, that tells you what size jet you have now,,, you need to purchase 2 bits,,,, one bit will be 3 sizes larger, one will be 5 sizes larger, than what your stock jet size is,,, A drill press wors great in drilling out the main jet,,,, take the 5 sizes larger bit, and drill out the main jet to that size,, DONT go too deep,, you can drill thr the casting anbd ruin the bowl,,, so just enough to go thru the brass,,, Blow out the shavings with air. Then, with the drill bit that is 3 sizes larger,, you drill out the bottom 2 holes of the metering stem. The metering stem, usually have 6 holes along the sides,,, your only drilling the bottom 2 holes,,, The reason for the bottom holes being drilled is, to keep the holes below the fuel level in the carb and will be supplied with plenty of fuel,,, if you drilled the top holes,, the float level can affect it by the level being too low, and fuel not reach up that high,,,,, Blow out the shavings,,,,, and reassemble the parts and install it back on the tractor. Id start with the main adjuster about 1.5 turns off the seat,, that should get it started,, warm up the engine,,,, and have an assistant open the throttle all the way, (while its running) and open up the main adjuster,, if you can make it stutter, smoke black out the exhuast from too much fuel,, you will now have enough fuel flow to feed your engine under a load,, BUT,,,, lets say you cant get it to run rich,,, go back to the store and get the bit that will be 7 sizes larger,, redrill the main jet size, if you still cant run rich,, take the bit that is 5 larger and drill out the bottom 2 holes of the metering stem again. it will get fuel to it for sure after that,,, but,, you want to start small and work your way up. At this time, Id run a compression test,, if its over 150 psi, Id step up to a 89 octane fuel,,, they run better on it,, if you cant get 89, try to stay under 93 octane,, Sure hope this makes it simple, get your parts book out and ID the parts I mentioned,,, its easy once you see how its done first hand. Need help, get ahold of me, email, or call, 574-893-7437. Good Luck! ChadS