Sputtering and hesitation

I have got a 83 kz750 k1 that i got for free and I know now why I got it for free. I had some problems with fuel delivery so I bought a pecock rebuild kit and that solved the problem, well sort of.
THe bikestarts up fine, usually after the first kick. (Starter doen't work too good) Idles fine a little rough but it is a twin so I can't imagine idling great. When I rev it and there is no load on the bike revs fast and sounds good. I get on the bike and it doesn't want to do anything but sputter. I replaced the gaskets in the petcock. I put a new battery on it. Cleaned the carbs and changed the oil, air filter and plugs. It still does it, but not as bad. If I am accelerating slowly runs fine, the instant I open up past a quarter throttle, it sputters, but never dies. And then after sputtering for a few seconds, it starts to accelerate. At higher speeds it does good. Like around 4500-7000 RPM's. Even at idle to about 2000 it seems to do ok, but there is that speeed in between it doesn't seem to do anything but pisss me off. I am thinking about doing a complete carburetor rebuild as I know one was never done on the bike.And like I said it is an 83 with 29000 miles and it sat for a good while before I got it. Also it didn't give me this problem when I first got it. I cleaned the carbs and it ran great, didn't hesitate or sputter at all. This problem came after I rebuilt the petock, whick I pulled off the fuelline while it was running and it was pumpig fuel fairly steadily. Wasn't lots of fuel but a good stream. I am thinking about driving this bike off a cliff, but if anyone can help with the problem I am having, that would be much aprreciated.

You say you cleaned the carbs and it ran great. Problem started after rebuilding the petcock.

Did you put a fuel filter between the petcock and the carbs ? Fuel filters are great. You may have gotten some crud into the carbs and may have to clean them out again.

Hopefully you will get additional advice from others more experienced than me.

Andrewpost

Did you ever figure this problem out? I have the same bike and the same exact problem.

One possibility is jetting... if it's running ok up to quarter throttle but stumbling above that without smoking... you could be running lean on the main jets... try going up one size on the mains especially if you are running any kind of aftermarket exhaust or aircleaner...

Went from 115 to 117.5 should I go to 120?

Are you running pods or the airbox? I was having a similar problem, w/pods, until I drilled out the diaphram slide hole. Another possibility is that the slide may be sticking.

Amy idea what the black coating is on the slides ? or is this a PO thing someone did to my bike ? The later twins run lean , I raised the needles when I got the new mufflers on still a little lean though .. will work on it soon as the cooler weather seems to be here now .. (:

Stock air box on my 83 twin. The hesitation seems to get worse when I put larger jets in or raise the needle with a washer, but still needs the choke out to run.

What shape are your intake manifolds in. Sounds like a big time air leak between carbs and engine.

I believe they're in good shape and connected well.

Is this a vacuum actuated petcock??
You may have air infiltration at that point.