Is everything ok with the cap and rotor so that the spark is getting to the plugs? Those carbs are pretty reliable. Is the choke cable hooked up and working? The regulator that is mounted in the thermostat housing drops the lp tank pressure down to about 15psi and that is what should be entering the carb. When the regulator fails, the pressure will go up and cause a a very rich condition that would cause it not to start but you would probably smell it. I would check to make sure each spark plug is getting spark and at the right time if it's not showing any signs of firing at all during cranking.