1978 kz1000a renew and revenge project

I guess I could have did a better job at explaining what you see. In the sequences of pictures its starts with carb 1 then 2,3,and 4. Red in the AFR curve will be anything above 14.7, green is anything above 12. The sawtooth waveform is from giving it mid throttle and releasing over and over again.  

What you can see is that in the first set of pictures, carb 2 and 3 would go lean on mid throttle. I moved the clips 1 position down which lifts the needle all the way up on carb 2 and 3. The second round of 4 pictures shows all 4 carbs responding to the throttle by going to an AFR of slightly above 12. The concept is to have the bike idle at 14.7 for efficiency and enrichen to 12 for power. It looks like it worked out pretty well.

So in summary, Idle afr is yellow of something below 14.7. I give it throttle and it goes green, which is something above 12. It’s synchronized and responds to throttle like any other performance motor Ive had. I could take pictures of the plugs if anyone is interested in reading the salts.

Thank you gentlemen for the explanation and the manual. 

paint looks great. nice work. 

Forks cleaned up, clear coated and rebuilt. New rotor, new wheel. I have also discovered that the forks are bent but someone had mounted them in a way that kept the wheel straight.

The bike is able to be ridden so it’s time to start tuning WOT and mid on the carbs. Here is the status and suggested remedy that I will implement soon.
October 5 2025 (idle jet, main jet, Clip on needle)
#1-idle perfect, wot is 9.4 AFR, mid is rich (15,122, 2)
#2-idle perfect, wot is 9.4 AFR, mid is rich (12.5, 122, 1)
#3-idle is perfect, wot is 9.4 AFR mid is rich cruise is super lean (10, 122, 1)
#4-idle is perfect wot is 9.4 AFR mid is rich (10, 122, 2)
Remedy
take all mains to 117 jet
look at #3 low mid needle jet
 

I used Chat GPT to calculate the right main jets. I measured the distance from the AFR curve to 12.6 and told it all the main jets i had. It calculated the new jet and its within 1 jet size (probably the error is me using calipers to measure distance on my phone). and considering it made a jump from 115 to 98 I was skeptical. The AFR was 9.6 to start and if each jet size is 4% thats allot of pulling/putting main jets in and out. I would say it nailed it.

 
(carb #, current main jet, current conditions, next change)
#1 (98) cruise is way rich stumble on transition but wot looks perfect go 100
#2 (98) cruise is a hair lean and wot is 16 at 7k but is perfect at 5k go 100
#3 (105) cruise is lean idle a bit lean transition lean wot a hair lean go 107
#4 (105) (suggested 107) cruise is too lean and stumble going to wot, wot is maybe perfect or a hair lean maybe go 107

current status of all jets

#1(15, 98, 2)
#2(12.5, 98, 1)
#3 (10, 105, 1)
#4 (10,105, 2) 

Remaining issues

A-all cylinders stumble from tip in cruise to WOT. I’ll check float fuel level and move it to 2mm.
B-I also ordered a pingel petcock
C-I will check that the tank is venting properly
D-All cylinders have a slight lean condition at max rpm so I will increase the mains 1 level on main jet.
E-cruise is lean on all cylinders except #1. I will go 1 richer on 2-4 and lean #1 (needles)
F-all idle between 12.6 and 14.7. I can confirm that changing mains does very little (or nothing) to the AFR on idle.

 

With AFR above 13:1 at on an air cooled motor is it not going to get really hot during prolonged idle in traffic ?

I would have to default to your opinion, Im just a visitor here. What are your thoughts? I can always make changes later, it’s not like im going to ride the bike allot. Im just using rules of thumb from tuning cars until someone gives me a better idea. 12.0 for power, 14.7 for economy, 15-16 for no load idle. 

bry195 wrote:

I would have to default to your opinion, what are your thoughts? I can always make changes later, it’s not like im going to ride the bike allot. Im just using rules of thumb from tuning cars until someone gives me a better idea. 12.0 for power, 14.7 for economy, 15-16 for no load idle. 

My opinion (and that's all it is) would be that on an air-cooled carb motor between 12 & 13 throughout the rev range is a "safe" setting (this is what I will be aiming for on my build when it comes to set-up) the rational is that whilst a stoichiometric 14.7:1 (lambda 1) is recognised as the ideal, you need to remember that in the car world this is controlled by sophisticated electronics and a plethora of sensors measuring temperatures and pressures of every function. If temp starts to rise or "knock" is detected the ECU is making continuous adjustments to fuelling and ignition. A stationary air-cooled motor will get hot relatively quickly which would be accelerated by a "lean" mixture, likewise on a cold fresh morning the mixture will also lean out as the intake air is denser. Most cars produced in the last 30 years are effected to a much lesser degree by atmospheric changes due to engine management electronics and pretty much all are "water cooled". 
I read somewhere that some competitors in the "Carrera Panamericana" carry a spare set of carbs with different jetting because of altitude changes (changing the carbs is quicker than changing jets) and with events like "Pikes Peak" the carbs are set for about half way up as a compromise to changing air density due to altitude. Carbs will always be a compromise 

All very much appreciated input. I’ll tighten up the idle target to below 13. Changing the main jets doesnt seem to make allot of difference to idle but I’m moving to needles next and it might. I made sure that i achieved the intended idle afr with plenty of room on both sides of the pilot adjustment. 

it really is kind of amazing that a carb is as resilient as it is. Each carb has 3 circuits and there are 4 carbs. You have fuel flow, level, temperature, pressure. Thats like 4^7 ways they shouldn’t work.

My understanding is that the idle is purely controlled by idle jet and mixture screw - idle to 1/4 throttle is the pilot circuit - 1/4 to 3/4 moves onto the needle and main jet - WOT is purely the main jet so changing the main won't effect idle mixture

Makes sense. if you look at the curve between 5 and 10 seconds you see the WOT pull. its targeting 12.6. it tips in lean and goes lean towards max rpm. the dotted line is 14.7. When I let off (right ant lean) it goes rich. All 4 carbs look this way to varying degrees. This screams of a common problem. Do you have any thoughts to share?

Common problems
I think i set all fuel level to 0 instead of 2-4mm, except one I didnt adjust at all and its probably floating at 6-8.
my petcock leeks and got a poor man’s rebuild
gas cap is brand new chinese. need to confirm it vents.
quick connects and fuel filters on the fuel lines to carbs
(I can probably take a shortcut and see if i can deliver a liter per minute of fuel)

tip in specific problems
fuel level
carb cutaway
(?) needles to lean
(?) oblong needle seats.