1949 Model A Help

I am looking for some ideas with trouble I have had with a 1949 Model A. It sat for two years not being ran. I decided to get it running again. I put a new battery, points, condenser, coil, rotor, plugs, cleaned and rebuilt the carb including drilling out the passages. The moment of truth came and it started and ran well. I drove it around the property and it didn't miss a beat. The next time I started it, it ran rough with no power and was missing. My first thought was the carb so I cleaned it again and it still didn't run great. I went ahead and put new points and condenser on it and then it ran great again. Same deal next time I went to start it it ran rough. My thought at this point was that sediment from the tank was making its way into the carb. So I took the carb off again, cleaned it and then installed a fuel screen extension in the top of the sediment bowl to prevent anything from the bottom of the tank from getting into the fuel system. After doing this it ran great again. I ran it for a few hours last night and then ran it again another 3 this morning doing some grading to my drive. I parked it for less than an hour and then it did it again. It was missing and had no power. It wouldn't even make it back to the garage. I did it all again, new points, condenser, spark plugs, and cleaned the carb. I have blue strong spark, I am getting fuel and now it does not want to start. I am at a loss as to why my issues is so intermittent and what could be causing it. One time it will fire on the first crank, the next it takes quite a few and then runs rough. Any ideas would be greatly appreciated!

What are you running for fuel in it. I
had my 39 l that has always started good
only to after it sat for like 2 months
not want to start. We even pulled it an
no start. It has good spark good fuel
running out the drain plug of the carb.
Found out that the 87 gas with the 10
percent ethereal the water in the fuel
sat on the bottom from the fuel. I ran
the fuel in a pan tell I could smell and
see the sediment bowl change color from a
creamy white to the gas color. After that
4 turns of the crank and it was running
but it stumble some. Now I run premium in
all and they run so much better.

If you do two or three things to the tractor and the problem corrects, then
what corrected the problem. You don't know. Do one thing at a time. You
can tell a lot about your engine with a compression check. What was the
condition of the plugs when it started running rough? What did the exhaust
look like? Might try running a hotter plug.

I tried them one thing at a time and then reversed the order. After doing some more digging on it I think it is a charging issue. Once I run it a while the battery (which is new) drops in voltage. Once it sits a while the battery recovers and it will run fine. The plugs have been coming out pretty black which would signify running rich, but I only get black smoke once it starts running rough. My theory is that the voltage is dropping at that point resulting in weaker spark and fouling the plugs. It sat overnight last night and then fired right up. I am getting sporadic voltage readings at the battery while it is running. It sat most of the day today and before starting it up the battery read 12 volts. After letting it run for five minutes, I turned it off and battery read 11.92.