Motorcycle Repair: Overheating? Rejetting?, jet sizes, cb750k

Question
email:bserdy@tds.net
Hi,
I bought a 1980 cb750K that has aftermarket 4 to 1 exhaust with a megaphone style muffler. I rebuilt the carbs because it would not idle below about 2000. I bought carb kits and I used a gallon can of carb cleaner from Autozone. They are clean now and it will idle at 1000 with no problem. The air box and filter are stock. I just replaced the ignition modules and one coil (the modules had melted and one coil had split - the secondary was open). Ignition is in great shape now - blue spark. The problem is as follows: I start the bike and it idles fine, I take off smoothly and go through the gears shifting at about 3000rpm and no problems. I travel about 1/4 mile then stop at an intersection and start off again and no problem. I now travel about 3 miles at highway speeds and slowdown for a turn. I travel about 3 city blocks and now the bike won't idle and responds roughly to the throttle. It even seems to be running on two cylinders. I limp home at low power. There is some pinging when starting from a stop. It will not idle. Let it sit for about 15 minutes and it starts and idles fine. I can repeat this scenario over and over. The timing is ok. The bike really flies on WOT. The jetting is the original size: primary 68, secondary 102. Does this seem like overheating? Should I increase the jet sizes and if so what should I try?
Thanks in advance,
Bill  

Answer
Ok, here it is.  Your problem is quite normal!  First of all what kind of 4 to 1 did u install?  Here's the problem:  The bike is lean and in-change is causeing a carb vaccum issue.  When u changed the exhaust u needed to install a .112 sec. jet.  Your pilot jets need not be changed at this time.  Did the bike run fine b4 your install?