Check your compression first, then your carb diaphragms. If they're worn or cracked, that could be your biggest problem (dumping fuel down the carb will help determine this). Check the battery or charge it up if it's low. Lastly, check the plugs. If they are dirty, hazy, or damaged in any way, replace them and try again. Remember: Fuel/air, compression, and spark is all you need to get it started.
Are the plugs getting any fuel on them (e.g. is it flooding the engine after cranking it for a while)? I would troubleshoot your fuel delivery problems all the way through as well as doing the compression check. You can buy a compression checker for $15 or less at any automotive place in town, so it's a cheap piece of equipment to buy, but you can use it on anything after that.
Have you cleaned out your carbs at all? Even if it costs you the gasket set, I'd think that simply knocking the 'dust' out of the carbs (e.g. varnished fuel, oil, and dirt/debris) will solve a lot of problems. Check your jets while you're in there and make sure floats, needles, jets, filters, or any other assemblies that are in there are completely clean before re-installing.
Are you getting spark on both plug wires? You may be getting spark, but is it enough? Not sure if yours runs directly off the magneto or if it's coiled, but it could be showing spark on the outside, but not be strong enough to light up the fuel.