Well, let eliminate a thing or two. If you are having starting problems it could be a lot of things, but lets check the simple things first. while the tractor is running at above 1500 with a good digital voltmeter, measure the charging voltage on the battery terminals. It should be near or above 14 volts but less than 14.5. If you see something like 12 or anything less than 13 you likely have a alternator/regulator problem. If the charging voltage is good and if the battery is good, then you really could have a starting issue, or a connection issue. Does it try to crank but does not spin very fast and not start? that could be low battery voltage or a high resistance connection. Try to measure the voltage directly on the terminals of the battery not on the cable terminals but directly on the battery terminals while someone else trys to crank the engine, if it drops below about 10.5 volts you either have a very "draggy" starter, ie it draws lots and lots of current or the battery is no good. in that it has a high internal resistance. or a connection problem (hi resistance) replace battery, or get one of the starter current meters, which actually measure the magnetic field around the starter wire when cranking. you just hold it up against the wire and it will give you a approximation of the current draw of the starter. Now if the voltage stays up on the battery while cranked, but the engine does not crank you likely have a connection problem. leave the negative lead of the voltmeter on the negative terminal of the battery and measure the voltage on the battery cable terminal. if it is low, you have found your problem at the battery terminal connections. or it could be in the starter cable internally (usually corrosion inside) or further along to the starter, in otherwords start at the battery and work back. If you dont have a good digital voltmeter (prefered) you can do quite a bit with a testlight if you are good at interpreting its brightness (engine off reading vs running ) etc.
Please get back to us and let us know what you have found. Many of these problems are very simple but can be very frustrating.
James K0UA