Too Lean?

• Rack one will have stock needle jet setting, but a 5 to 10 point larger main jet. Most likely will start at 120.
• Rack two will have move needle jet clip from 3 to 4, raising the needle for richer, stock main jet at 110.
• Rack 3 will be a mix of the first two. Needle jet at 4 from top, main jet at 5 over at 115.

• Bike starts easily from cold. Just a tad bit of choke, instantly fires. No cranking needed. When fired, she can run off choke at idle with just an occasional hiccup as the engine warms then settles in nicely after only 1 or 2 minutes. To me this indicates the pilot circuit is properly jetted.
• If not 'romping and stomping', the plugs come out much darker. Cylinder one is still leaking a bit of oil into combustion process, but it's tolerable.  That tells me the pilot/needle jet circuit is good up to main jet / needle jet transition point. In other words, from 1200 to 4000 rpm, the plugs look normal.
• From 5k and up, on extended durations, the plugs come out white. To me this indicates too small main jet. Additionally, this is 1 overbore engine running DG 6-1 exhaust. Stock air box. Upgraded coils and wires.

Kawboy wrote:

If you look at your 2 spark plugs with different heat ranges, you'll see that the hotter plug has a longer ceramic cone around the center electrode compared to the colder heat range plug. The longer the ceramic the further the heat has to travel to get to the spark plug base to disapate the heat through the spark plug base and to the cylinder head. Hotter heat range plugs than the standard for an engine were designed for the "Granny's" out there that get in a car and drive to the corner store and drive home and don't get the engine up to temp. If you don't get the engine up to temp and run it for 10 -15 minutes, all the carbon that built up on the spark plug when the engine was running rich on semi choke would not burn off and plug fouling would occur. Hotter range plugs will burn off the deposits under light loads more so than the engineered range plug for that engine.
On the other hand, colder range plugs are used when the engine is running under full load more than cruising mode like on the race track. If the ceramic around the spark plug gets orange hot to white hot, preignition will occur causing detonation and detonation in the presence of high cylinder combustion chamber temperature will blow a hole in the piston.
I normally think of pre-ignition as 'knock' noise, or detonation. Having just used the powers of AI, now know PI can occur without audible 'knocking'. Scary!

With all that being said, the BPR6ES spark plugs are the proper heat range by design for the "normal" use of the KZ1300. If that's the "standard" then something else is causing the white ceramic shading of the ceramic on the spark plug. Putting in colder range spark plugs is putting a band aid on the problem and not getting to the root cause of why the bike is running so hot and bear in mind you did note that the bike was running like a Banshee like your KX500 just before it blew up and that's a true " seat of the pants" experience of preignition.
Your comment triggered me, but in a good way ... This engine is not stock, or 'normal' anymore. It's 1 size overbore, running a DG 6-1 exhaust, no crossover.

If you ever played around with glow plug engines used in model airplanes you know exactly how preignition works because that's the principal of the ignition of the fuel in those engines. The glow plug is initially heated to orange hot with a battery. Once the engine starts and "warms up", you then remove the battery lead to the glow plug and the combustion of the engine sustains the orange glow of the glow plug. Once up and running, you open up the throttle and then adjust the fuel mixture to achieve the highest rpm. At that point, if you were running the engine without a muffler such as with the Cox .049 engines, you could see in the exhaust port and see the orange glow of the combustion to almost white hot of the combustion. The goal was to run a nice orange because if you ran closer to white hot you could burn out the glowing coil in the glow plug and then the engine would die and you would then have to replace the glow plug. Not a problem on a tethered plane but on a radio controlled plane, you might be walking a mile to retrieve your plane.
Still have a couple of engines from 'back in the day'. What I didn't realize is the glow plug continued to glow after adequate combustion temps were achieved. Until now thought they just 'dieseled' due to high compression and speciality fuel.

I've been fascinated with internal combustion engines my entire life since I was 6 years old and I never stop learning what I can regarding the science and technology behind these engines. An even more fascinating subject is now showing up in electric motors since the advent of electric vehicles . Radial flux motors versus axial flux motors. The pros and cons of each - fascinating !! 

How about Koenigsegg's electric motor  Dark Matter electric motor   86 lbs producing 800 HP and 922 Lbs/Ft torque. Put that in your bike and smoke it !!

If any of this tweaks your interest you really have to check out  The Koenigsegg website  and see what's possible when you're a crazy German Engineer with buckets of investment in your company. I would die and go to Heaven for an opportunity to work in his facility.

Thanks for the tip, will check it out. I also enjoy Kevin Cameron's discussions in Cycle World.

Enjoy,
KB