H died and I can't figure out what's wrong

I am hoping someone smarter than me can tell me what I may need to do to get my H back to running. I have been using it lately to haul wagons and such and this morning I drove out across three fields to some woods, parked the tractor, went in and cut down some trees. When I got the tractor to drive it in and pick up the wood it was hard to start and seemed to be running on three cylinders most of the time. I went ahead and drove it over to the trees and loaded the wagon. Went to start it again and it would only fire on two cylinders and then died completely. I found that the sediment bowl had a lot of rust in it, I presume maybe from driving across the bumpy fields. I dumped it, cleaned the gas line out, took down the carb, cleaned it as best I could and put it back together and still nothing. The spark is good, the suction on the air inlet is strong. I pulled the plugs, #1,4 were dry and #2,3 were fouled. I'm wondering could I have gotten rust particles somewhere up in the intake, or could the carb have a problem? When I cleaned the carb out I noticed that the slot headed shaft on the bottom front corner of the carb is broken inside, at a point where the seem to be four little holes in the shaft. I'm wondering what that is and whether it could keep the tractor from running? I am sorry this is so long, I'm completely stumped. Any advice will be very much appreciated.
Zach

You may have fowled the two plugs. Clean fuel lines might flow, but if there is crud in the tank where the inlet is located, it will not get to the lines. There is a screen at the fitting at the carb that is also prone to collect rust.
If the fuel comes out as fast as through a small sweetheart soda straw, it should be fine. I have seen trash on top of the needle and seat restricting flow. Check the manifold for tight mounting as well. Jim

Thanks a lot. I'll get out there in the morning and check the manifold and change the plugs. I have good gas flow out of the bottom of the carb but it doesn't seem to be getting into the engine. I thought there was supposed to be a screen in there but I couldn't find one. I appreciate your help.
Zach

Slot headed shaft at lower front of carb, hummmm. Sounds like the metering nozzle nut and if the nozzle is cracked it will not run well as they are your air bleeds that change the mixture as the venturi vacuum changes when coming under varying load. Maybe I am not understanding what you are putting down though.

Thanks, I'll take a picture tomorrow, or two. It looks to have been that way for a while, maybe. Is it possible to find a replacement or would I need to find a whole new carb to address the problem?
Zach

You probably should pull No1 plug and bring No1 piston to TDC on the compression stroke. Once you have No1 at TDC pull the distributor cap and see where your rotor is pointing. Should be at the No1 plug tower. Take a good look at your cap to make sure there's no cracks. Hal