kz550 won't idle with airbox cap

Hey everyone.
I just got the air filter cap for my 81 kz550 today after removing the pods and putting the air box back on. The bike will start and idle with the cap off but when I screwed it in the bike would idle poorly for a few seconds and die. It also dies when I twist the throttle. The previous owner put pods on the bike and when I took them off they had a small amount of rust on them as if they were being run on the bike, however with the pods installed I couldn't give the engine more than 1500 rpms or it would stall. I figured the carbs weremt jetted to run with the pods and bought the air box but it seems like with the air box the carbs aren't getting enough air. Any suggestions would be appreciated
Thanks

I would start by checking the current jetting. If it's not stock I would set it to stock and see how it runs. Ed

Thanks Ed.
This is probably going to be a stupid question but I'm new to motorcycles and mechanics in general. How do I get the jets out of the carbs to check the sizes?

You probably should have the manual before you start that process as it contains much info that will be helpful. Ed