TOPIC:

1982 KZ750M1 CSR-I had to replace the pipes and changed from 2 into 2 to a 2 into 1. The bike runs terrible. I can't get it to idle and when running will stall as soon as gas is applied. I've adjusted air screws and this hasn't helped at all. I'm sure the main jets need to be replaced but I don't know whether to go up or down in size. Kawasaki parts list shows the mains as 115s.
There is no larger size shown. The next down is 112.5.
Any suggestions? I appreciate the help.

Contact WiredGeorge (a member here) and ask him if jets are available, I don't believe they are, but he may know of others that may work.

You might want to disassemble the carbs and clean them, it sounds like your idle circuit is clogged. For the main jet, you might see if you can put a small washer under the clips on the needles to raise them up a little.

bigger main jets are required
did this bike run before the pipe exchange??
recheck the basics: fuel delivery,fuel level,timing, synchronization. battery charge level all the simple stuff for starters.
you have to get the mixture screw to a point where it does effect the idle. (float height adjustment)

are the pilot circuts clean?

these bikes are prone to electrical problems in the ignition systems also
just changing exaust pipes do not cause that many problems. it will magnify exisistng problems

I have replaced the stock 2 into 2 exhaust with a 2 into one on a 79 and on a 80 750 twin, and both ran fine on the stock jets.
But both the 79 and the 80 have 125 main jets stock, so maybe the 82 is set to run leaner for emissions reasons and the 2 into 1 pushed it over the edge. I still think your carbs need a good cleaning though.
Since the 82 has electronic ignition there is no timing adjustment, but you should still check the resistance of the coils/plug wires/plug caps, and make sure the valve clearance is within specs.

Didn't get enough info to guess what jetting might be needed. Is the stock airbox still being used or are pods on the bike? Jets are standard Mikuni fare... regular large head mains and BS30/96 pilots.

Sorry for the delay in getting back. The bike ran fine before the pipe change. It has a stock airbox. I wish I could check if syncronized but it won't run long enough. New plugs are installed and I have good spark.
The needles on this are NOT adjustable. Float seems to be at correct height.

There are no additional grooves on the needle to allow you to move the clip. but you can put a 1mm thick washer under the clip on the needle to raise it 1mm.

Bigger numbers equals more fuel flow, 125 flows more fuel (makes the mixture richer) than a 115.

But it don't make any difference anyway, your problem is in the idle circuits if it's a carb problem, the main jet does not enter the equation until you get to somewhere betwwen 1/4 and 2/3 throttle (I forget the exact numbers). Take a look at the needle, it does not begin to taper (to allow fuel to pass) till somewhere near 1/2 it's length.