6 volt or 12 volt?
Donít guess at the cause of the problem; guessing can get expensive. Troubleshoot the problem.
Check for spark and fuel immediately as soon as it won't start.
You need to answer 2 questions before you do anything else:
With the bolt in the carb bowl removed and the gas on, will the fuel flow fill a pint jar in less than 2 minutes?
Next, get out your adjustable gap spark checker * , open the gap to 1/4", hook it up, turn the key on and crank the engine. Does the spark jump 1/4"? Post back with the answers.
And do not buy a new part for the tractor until you can answer this question: how do I know the part on the tractor is defective?
* Don't own an adjustable gap spark checker? Buy one! Not a test light! Until then, take an old plug, open the gap 1/4" ground it to the head & look for spark. Itís not the color of the spark that counts; itís the distance it jumps.