Number 1, never fire a 2-stroke engine on starting fluid. The oil in the fuel is your only lubrication and you should be a using a squirt bottle of pre-mix fuel into the throat of the carb when trying to troubleshoot a no-start condition.
You need to go down a full check list as Racerone has suggested.
1) Does the spark jump 3/8" gap with an air gap tester?
2) Do you have the proper
QL78C spark plugs installed?
3) What are your compression values?
4) Are you getting fuel to the carburetors?
5) Are you using the proper starting sequence?
Please verify all these and report back. It's possible the timing is off but you could have an issue with one these other things I've listed. Also, if the carb linkages aren't properly synchronized that can cause starting issues too.
KJ