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2025-03-19 Kz1300 Spark Plugs

dcarver's picture
published by dcarver on Thu, 03/20/2025 - 11:40
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1979 KZ1300 A1 Kawasaki

 

2025-03-19 Spark Plug Check

Noticed yesterday on ride that she seemed a bit lean at near full rpm e.g. main jet circugit.

Pulled plug for a look.

Cylinder 1 is far and away the worst looking plug. Not sure why it's black around diameter.
Oil consumption has dropped to *nearly* zero, but me thinks cylinder is the burner.

1-6, L to R.

From my POV, 4 is optimal followed by 6. Worse is 1, 3.

Another lineup, with electrodes reversed.

Thinking about running a slightly colder plug, BP8ES on 2 - 6.

Of course, this is running around at sea level, and pretty sure this motorcycle will never receive death Valley or lower elevations. Still, I sure don't want a hole or piston.

Note: Stock jetting, but 6-1 DG Exhaust.

 

Submitted by dcarver on Mon, 05/26/2025 - 11:32.

Noticed yesterday on ride that she seemed a bit lean at near full rpm e.g. main jet circugit.=14pxPulled plug for a look.
Cylinder 1 is far and away the worst looking plug. Not sure why it's black around diameter.
Oil consumption has dropped to *nearly* zero, but me thinks cylinder is the burner.

1.jpg

From my POV, 4 is optimal followed by 6. Worse is 1, 3.

6.jpg

Thinking about running a slightly colder plug, BP8ES on 2 - 6.

8.jpg

 Of course, this is running around at sea level, and pretty sure this motorcycle will never receive death Valley or lower elevations. Still, I sure don't want a hole or piston.

Note: Stock jetting, but 6-1 DG Exhaust.
 

9.jpg

Back from the work gig. Did some romping and stomping on the mighty KZ, including some pulls to full red line. Ran here in 4th on a slight uphill at 5k rpm for about 2 minutes, hit the kill switch, coasted to trailer, let her cool then pulled plugs. Me thinks too lean. Also, at full song, she kinda felt like a 2 stroke kx500 I had right before seizure.. Kind of hard to describe, but just a feeling of too much power for throttle setting.

Anyway, good to be back and hope all is well in your world!
 

Pic 1

KawBoy

Yup, running way too hot for a carbureted engine. I'm starting to wonder if the bikes that are running white hot are having fuel flow issues and leaning out when pulling heavy at high speed causing the float bowl fuel levels to drop which will lean out the mixture. Just putting that out there for thought.

Although Kawasaki doesn't have a "spec" listed for fuel flow testing, it can be worked out. In general, 1/2 pound of fuel /hour / horse power is a good general number to work with, so doing the math, 

120hp x .5 lbs fuel = 60 lbs/hour.
A US gallon of gas weighs 6 pounds, so 60 lbs/hour / 6 = 10 gallons / hour.

So let's say you wanted to do a fuel flow test. a reasonable time for the test could be 30 seconds. 1 hour  (60 minutes) / 1/2 =120.
1  US gallon = 128 ounces
10 US gallons = 1280 ounces 

1280 ounces /hour divided by 120 = 10.66 ounces in 30 seconds.

Bottom line - If you popped off the fuel line at the carb and did a fuel flow test for 30 seconds, you should be able to collect 10.66 ounces of fuel ( or more) to sustain 120 horse power without leaning out.

if the collection after 30 seconds is less than 10.6 OZ then either the fuel strainer in the tank on the fuel shutoff valve or the inline fuel filter is clogged or the vent to the fuel tank is blocked and you could test for this by taking a fuel flow test before the inline filter to eliminate the inline filter. If the flow is still to low, then the next would be to  confirm the vent tube in the fuel tank is clear. There probably isn't a way to remove the fuel strainer on the inlet of the fuel shut off valve without damaging the strainer, so I would say a very careful inspection of the strainer with a light and a magnifying glass may be in order. Remember that the purpose for the fuel strainer is to trap debris that could enter the tank so that the debris can't harm the fuel shut off valve seal faces. It's not there to remove debris for the specs required to flow through the passages in the carb.

That's my 2 cents ++++

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hope everyone appreciates KawBoy'z analytical engineering approach to form, fit, and function. Just look at his last post! He says he's a machinist or millwright or something, but we all know KB's an Engineer!

...and why, I wonder, why did the original engineers decide to use the unit of 'pounds per hour' instead of 'gallons p/h' or whatnot? Did it come from aviation where fuel weight is crucial to flight?

But I digress...

I ran two timed tests yesterday using the smart phone clock and a RatioRite measuring cup.

Test one was with the tank about 25% into Reserve, with the Pingle in reserve position. Here's the result.
 

1.jpeg


~15 Fl Oz in 30 seconds, acceptable. Even good, perhaps, given on Reserve and associated reduced head pressure.

I was all happy n' crap with results, then the thought crossed my cranium scarebellium...

"The Pingle has two separate flow paths, Normal and Reserve. You were on 'Normal' when running at 5k prior to shutting the engine down and pulling plugs for readings."
Acck!

Of course, this was AFTER I already had buttoned everything up, removed bike from lift, placed into trailer for ride today.

[img



Science, of course, requires due diligence so back on the rack for the "normal" test.

This time, the entire Ratio Rite filled to the tippity-top  in less than 20 seconds. Way plenty fuel.

Just for a lark, installed BP8ES plugs, replacing the BP6ES (colder). I don't yet fully understand spark plug heat range vs plug reading and impact of colder plugs on a lean fuel ratio.

KB, appreciate you, really do.

~d

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KB

Re: Too Lean?

1 day 19 hours ago
#33748
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.

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.

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.

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.

Enjoy,
KB
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Agree with the bandaid response. Forgot to mention 2 days ago, when performing flow rate test, also checked intake boots for snugness. All appeared to be snug. Did not spray WD-40 or other flammable liquid around the boots to check for leaks. Also checked each of the 6 vacuum ports for snugness. No WD-40 test.

Rode it for almost 200 miles yesterday, paying attention to not press to hard. Yesterday's ride was more about seeing how the bike rode sans the big flat slab of plexi known as a windshield.

Unfortunately, wasn't able to replicate the 5k run, kill switch to off, coast to trailer, pull plugs trick. My favorite public parking spot which enables it had a trespasser. Don't they know who I am?

I need a more scientific l, systematic approach. Establish a baseline via consistent testing. Change one parameter at a time, observe changes.

When it cools down in fall, I'll trailer the KZ out to my favorite long, straight, slightly uphill test road where there is zero traffic save for the occasional cow. I'll go with 3 different carb racks, each one jetted slightly differently than the other.
  • 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.
Testing will take all day, so I'll need t start early. Acck. I don't early.

Other notes:
  • 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.

Just thinking out loud...

We are starting hot weather season meaning the KZ won't get ridden much. I'll use that time to rebuild the other two carb racks I have and start the restoration of the second 79 Kz.

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Submitted by dcarver on Mon, 05/26/2025 - 11:51.

1 and 6 normal running e.g. 4k rpm and below.

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