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I have been having this issue since I got my 1300 on the road a few months back.I have been struggling with off idle hesitation. I have looked at other motorcycle forums and magazines of the period. I have played around with A/F mixture screws,color tuned,advanced my Dyna ignition for more low end torque,changed my spark plugs a few times ,changed spark plug wires,replaced my battery.Checked floats,raised my needle,increased the size of my idle jet,synced my carbs,checked compression,valves adjusted,new oil,checked timing,etc...I have a DG pipe on my ride.It screams on the highway but around town not sooo good. The only thing I haven't done yet is use compressed air to blow out the carbs since mine crapped out.The carbs were cleaned and gone through and rebuilt.I do notice the hesitation gets worse as the engine gets hotter.I don't want to turn this into a pissing contest.Only reply if you have experience with this and can help me,thank you.

Is your temperature stable.And your voltage.
And the needle height did it make any difference at all.

Temp normal for the 1300(hot and hotter that is)The electrical good I installed new stator and regulator as well and upgraded the lighting to led's and hid headlight and have a voltage meter and always in the green.I ordered the next size up idle jet(47.5).The carbs are coughing or spitting under hard acceleration. I have a feeling the ceramic coating on thr 6 into 1 is working too well.The company "Jet.hot" coats the inside of the pipe as well.I also need to blow out my carbs as well.I'll see if I can pick up a cheap air compressor to get me by in the mean time.

I typed a long response and as soon as I hit submit I lost it so here's the short version.

1981 KZ1300 with a DG pipe and a Dynojet carb kit. Was having the same off idle flat spot as you describe. Was also experiencing wet plugs at 1&2 and dry plugs at 5&6. Also had some surging between 3 & 4 K.

Where I am now:

Found fuel levels in the bowls way too high. Readjusted with wet method to about 1/4" below the bowl gasket.
96 mains
idle screws 3 1/2 to 4 turns out.
needles with clips in sixth notch.

The bike runs great. neither rich nor lean. Getting 40 MPG.

Plan for this winter.
Change up to 100 mains and drop needles to third notch.
Replace unreliable foam floats with Scotch's brass floats.
Reset fuel level by wet method.

That's my story and I'm sticking to it.

Bill

Thank you BTW I live at sea level what altitude do you live?Isn't coughing through the carb a sign of a lean condition?My plugs are good color as far as I can tell.I did order the brass floats from Scotch as well. Right now I'm running 115 main jets 45 pilot jets and at the 3rd clip in the needle. I started with 105 main jets and got a lot of popping sooo I went up to a 110 still alot of popping at WOT.Then I went up to 115 and it finally solved the the popping at wot.I also raised the needle to the 4th and 5th clip(dont have a sixth position)and might move back to the forth.Today is a crappy day here in NYC where I live sooo I will take off the carbs and install the new brass floats and move the needle back to the forth position.Next week when I get my bigger pilots(47.5)I will in stall to see if it helps with the off idle stutter.

I'm at 4000 ft here in Central Oregon. Dyna Jet recommends a smaller main jet when going with the DG pipe. Included in their kit are two sets of mains 96's and 100's. I believe the stock main jets are 110's.

Good luck

Bill