farmall 300 running a little rich

can i lower the level of gas in carb by adjusting float to correct this also serial # of tractor is 6437 DSJ and block serial # is 6440 D would this be original motor Thanks Bill

I would FIRST check that the choke is not partly blocking the airway and that the air cleaner is not restricting air flow.
Isn't there a high speed mixture screw on the bottom of the carb you can adjust?
Run the engine wide open and turn the screw in a little at a time until the richness goes away.

The mixture screw (bottom front of carb bowl) adjusts the load richness. It is not the main jet, it is a method of fine tuning the richness to meet demand at full load if working the tractor at near full power, and leaning it when using light loads. It can be adjusted in to make it lean enough to stumble when opened up, and rich enough to make it burn with a bit of black is worked hard. It should be played with a quarter turn at a time with the engine warmed up so that it just shows a very tiny bit of dark smoke when pulling at max HP/torque. If you are not working the tractor, it can be leaned so the exhaust is clean, but still goes from idle to full speed with no stumble. Jim

jim there is no adjustment screw on bowl of carb only screws are at the top of carb one is for idle speed is set for 350 RPMS then there is one on the very top of carb where it is bolted to the manifold would this be the one to adjust Thanks Bill

300 IH carbs are designed with a load screw. If yours is missing, that is the reason it is rich. The front bottom of the carb should have a forward pointing "boss" with a screw and spring and packing nut. (see diagram at caisih.com parts) below it on the same boss is a square headed drain plug. If there is no needle it needs one. Jim

Jim looked in my parts book it shows it with and without needle valve note says it should have one for gasoline like you said will have to find one any idea were i should look do you think case ih would carry one Bill

Be sure the carb has not been ""modified"" by someone, before you go to find a needle packing and spring. Bates will likely have it. As might the dealer. Jim
Bates

Bill your 300 originally came without the load screw and a carburetor number 361525R91. Just has a plug in place of the packing nut at the bottom front facing forward with carburetor mounted on the tractor. Carburetor was jetted to deliver the correct amount of fuel for most conditions. After a certain serial number break IH changed the carburetor metering on the engines and the carburetor number was advanced to 361525R92. All of the R91 carburetors were supposed to get a change over kit installed and changed to a 361525R92. Not all got changed.
But if this is a new problem you may want to check that choke cable is moving the choke wide open and air intake restriction and after that for needle and seat leakage. Also sometimes ignition system and spark plugs can be marginal and make you think they are over fueled.
You can check the float level and see if its leaking gas into it. Guessing the its a needle and seat or float problem if no problem with loading before. Make sure float doesn't rub carburetor casting. If you have a R91 carburetor you need packing, packing nut and a screw to add one to your carburetor if wanting to try that.
That would be the original engine equipped with 5,000 foot pistons when new.