If you are certain that you have all the passages clean in the carb then you probably have a vacuum leak somewhere. If you can get it to run long enough spray carb cleaner or starting fluid around where you suspect a leak. Just be careful with the flammable liquids. Usually you can find a leak quick with this method.
The manifolds often leak at the seam where they are put together.. there are several threads on here where people have drilled out the rivets, separated them and resealed.
Good luck with it 
__________________
Jay
40 years of Using and playing with IH Cub Cadets!
Proud owner of the following:
Cub Farmall, Super A Farmall, Original, (2)70's, 72, 100, 102, 123, 105, 125, 127, 108, 128, 1450, (3)782's, Yellow 982, 1782, "Sam's" 2182, M Farmall and a #7 trailer
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