It runs perfect for about a mile. Then it would cough, spit, sputter, backfire and stop running. I can let it sit for a while and it will run perfect for a distance in proportion to how long it would sit. Now at this point I'm sure you are think "it's a fuel supply fool". NOT!!. I took fuel cap vent apart, Blew through the vent tube, checked fuel to carb bowl by opening the carb bowl drain screw and draining a gallon of gas out at a rate fast enough to supply a big block Chevy. I didn't tear the carb down because any problems such as this would act up immediately and forever. Ah ha!!! It must be electrical! I can turbo charge a jet ski, build a 1000 hp small block Chevy, install a supercharger on a 2015 F150, and a bunch of other stuff but I know nothing about electrical. I put a new coil on it ... no help at all. Changed out the ICU. That changed the symptoms but helped not at all. Now it will go the mile and keep on going provided I keep the rpms up. It will do as before if rpms are in the bottom 3rd of rpm range ... exactly where my wife keeps it. OK, now I'm stumped.

 

Check the charging rate with a voltmeter across the battery. If it goes over 15v when you rev up, your regulator has had it. The other part you haven't changed is the trigger coil, I guess it could be that but I would have cleaned those carb jets out with an air line, costs nothing and can't hurt. Other things it can be is an electrical connector getting hot and failing, very bad to find, burnt insulation or a puff of smoke can be an indicator of that.

 

About the 3 things that I can see on the schematic that I haven't looked at yet are the voltage regulator, pickup coil and air temperature sensor. I didn't know it even had one of those until last night. Thanks for the info on how to check the voltage regulator. Will do today. It gets too hot to touch. I don't know what is normal there.

 

I think I may have found the problem. Oil cooler fan is not coming on.

 

The oil cooler fan doesn't run all the time. I'm not familiar with the KVF but the KLFs had it controlled by a handlebar switch, you put it on if you thought the engine was getting hot. Most other makes use a car style temp controlled switch so the fan switches on if the normal oil running temperature is exceded. Most of these fans don't come on unless the bike is stood ticking over, or pulling a trailer etc, at low speeds.

 

These are thermostat controlled. I tried a new test today. After I checked the fuse (good) I ran wires straight from the battery to the fan. The bike ran just as before - good until warmed up. It runs fine at speed and it idles just fine but coughs, sputters, backfires and either moves or dies, usually the latter. Through all of this testing the fan still does not ever come on. It should come on and stay on most of the time as it did in the past.

While not a formally trained mechanic I did fancy myself pretty good at trouble shooting. I'm doubting my abilities and accumulated knowledge at this point.

 

Like I wrote above, I don't know a lot about the KVFs, so if the fan used to come on a lot and doesn't now, the thermostatic switch may be faulty. However I am a bit puzzled by your post as you indicate that you have wired the fan direct from the battery, so it runs all the time, but then wrote, "Through all of this testing the fan still does not ever come on." Have you tested the bike with the fan wired to keep running?

 

I connected the fan to the battery for a short time to test the fan. It worked perfectly. I rode the bike with it connected that way. The bike performed as before - perfectly for about a mile. At that point the bike began to perform as before. It will idle but act poorly if at all at slow speed. At that point I connected the fan back as it should be connected. I rode the bike some more. It performed poorly (barely rideable) plus the fan never comes on. I can't believe these 2 problems are independent of each other.

 

Even before fuel injection became the norm, many manufacturers started getting very complicated with their CDI systems, so it is possible the temp sender could be feeding bad information to the ECU. However if the spark is intermittent for any reason, it makes the mixture run rich as the fuel isn't being burnt properly, this will make the engine run cooler so it may not reach running temp. This would also apply if a carb fault made it run rich.

 

Huuuummmm .... now to find that pesky temp sender.....