The first thing is you will need to remove one of the 1-1/8 inch nuts that hold the energy cells in place. Drill clear through it but with a size drill that you can tap  it with a 1/8 inch pipe tap. You will need to go to your auto parts store and get a male adapter so you can plug your air hose directly to this. You will also need to remove the energy cell cap that is behind this nut. Grap the stem with a needle nose Vise Grips and put it out. You will need to do this for all 6 of them. Put the cap back on. Take the valve cover  off and loosen all the nuts holding the rocker arms down about 3/4 inch. This is so the valves can not open. Then pump air in each cylinder one at a time and see where the air leaks: out of the intake manifold, the exhaust manifold or the dipstick hole. Our fair is going on this week so I am hard to find this week. Send me your phone number and it may be easier for me to call you this week. I would also like a serial number of the tractor.  John