Choke

I have a 77 kz400 - just recently had a tune up, along with the carbs cleaned out, new spark plugs, etc. It rode great, then I didn't ride it for about a week (outside under a cover). Today, it would loose power unless I kept the choke open a quarter to half of the way. Any thoughts on what could be happening? After the tune up, it ran well both in the morning at 55 degrees and in the hot afternoons. Today was about 60 degrees. Can gas go bad and gunk up a carb that quickly? In previous seasons, it would sit for a couple weeks no problem, but I used to have it in a garage - would that make a difference?

I appreciate any help - I hate to bring it back to the mechanics and spend more money if there is a quick fix...

Do you have a new fuel filter in place? You could have some debris in one of the carbs.

Honestly if you just paid to have the tune up and carbs cleaned I'd take it back to the shop and let them take a look with the understanding that you already paid for this work once. It could be something as simple as a vacuum line came loose.