Help with a 1992 XJ600

I pulled my 1992 Seca 2 out of storage last march and it ran perfect. I got really busy and didnt get to play with it for 5 weeks and now it will fire right up and while its warming up each cyindler will eventually cut out and will not start after for a while. Iv tried a fresh tank of gas and the spark plugs and air filter are clean. The same thing happened last year. I checked the fuel lines, filters and pulled the bowls off the carbs and everything was clean. Through 2 months of frustration i found that the Canadian model spark plugs were installed so i installed the ones listed in the shop manual and it ran great until i whimped out and put the bike away in November.
Any ideas?

The Seca II is a BITCH to get started when it hasn't been run in a while. I have a 94. That's odd that it will fire and then die off, though. I honestly have no idea what would cause that, given the remedies you've tried so far. Maybe someone with a lil more "detective" experience can help you out.