KZ650 rough idle, hunting, pop and dies when hot

if the main jet were far too big, or the needle worn or wrong profile, might that mask any pilot adjustments?

That's the problem of jumping to the mains first. Get the pilot working first with the needle in the center, then go to the mains. Fine tune with the needles.
Steve

Stock factory setting for the nettle on a 650 is the 4th slot........ moving it to the middle would lean it....... maybe 17.5 pilots ?

Your chopped pipes and "cheapo" pods are the culprits. 17.5 is a good starting point. I would suggest your finding a decent exhaust for it. You can make it run but overall ridability will suffer. Dial it in with the needle in the middle position. IT'S NOT STOCK.
Steve

Right not stock but pods and a opened up pipe would want you to richen the nettle or at least leave it alone and not lean it out don't you think ?

KZB2, I would think normally yes. Opening the intake and exhaust would mean richer settings are needed.
But I'm not running lean, so I'm going to leave the needles alone until I troubleshoot everything else.

From what I've read, the needle position is fine tuning. I'm currently in the the troubleshooting/coarse adjust. phase.

I've cleaned the plugs and re-gapped to 0.71~0.74mm (0.028 to 0.029 mil)
I checked plug 1 after riding to work and it stayed clean, but near the end of the ride the idle started acting up a tiny bit.

I'm going to do the following tonight.

1. Check the fuel levels (I believe they're currently a few mm lower than spec)
2. Check the pilot system and air screws,

Though the jetting may not be quite right, I would first check voltage to the coils. It needs to be very close to full battery voltage. This is required to provide a good fat spark.. Sometimes black dark plugs are due to poor ignition and not an overly rich mix.

From what I've read, the needle position is fine tuning. I'm currently in the the troubleshooting/coarse adjust. phase.


Yup, just the needle profile/position affects your fuelling from when the main jet is just cutting in, all the way to WOT, also it is a quick and easy test if you aren't sure which way to go. Just feeling a slight difference, better or worse will help narrow down your problem.

Needle position makes a difference between 1/4 and 3/4 throttle, after that it is main jet only, hence tuning top down..

Also really you should be tuning top down: sort your main jet first then do the fine tuning. Slide carbs are easier to tune then CV's.

As above, often carb and ignition problems can be hard to differentiate.

An update. Short version: Fuel level on 3 carbs is 4mm, but carb #3 might have a float issue, plugs quickly carbon back up after being cleaned, and the air screws do seem to work. Operator patience needed.

I cleaned the plugs and checked their gap (0.028" to 0.029") before work yesterday. Rode to work and then back and the bike died just as I was coasting (clutch in) into the driveway. Plugs are already starting to go black. There's some oil on the threads of two, but mostly dry and black.

Also, the air screws do have an effect, I just wasn't patient enough to wait for the rpms to respond.
I believe with all the screws about 2 turns out I get the highest idle rpm.

I checked fuel level with both tires on the ground and shimmed the kick stand until a spirit level was level across the frame rails under the seat.

I measure 4mm below the carb lip for cylinders 1,2 & 4, and 3 mm above the lip on carb #3.
Obviously carb 3 is very high, though I'm sure all the float heights are set within 0.5mm.
This might explain the hot idle issues, but doesn't explain all the cylinders running rich.

I will next check battery voltage at the coil primaries, and check to see if I have a sticking/sinking float or valve.
I will also take the opportunity to run some compressed air and solvent through the carb passages.

My battery is low. but it has measured 12.6 to 12.5 in the recent past.

It now measures 11.6V, 10V with the ignition on, 9.7 with the engine switch on, and 9.5 at the coils.
So not much drop at all between the battery and coils.
I put it back on the tender. Perhaps my extended idling while observing the symptoms and carb adjustments drained it a bit?
When the battery was at 12.6 volts I was getting 14-15V at 4krpm and 3-4 amps.

While the battery is charging I'm going to check out the carbs,

Nothing definitive yet. I took the carbs off and made sure passages were open using carb cleaner and air.
Looks like the o rings on my air screws could use replacing.

Fuel level on carb 3 now measures 4-5mm below the lip.
I've noticed that if I set the fuel level any higher (float level lower) that the floats are bottoming out inside the carb body.

I put the charged battery in the bike and rode about 20mi of mixed speeds and some stop and go, but not much extended idle like at a long red light. After returning, the battery measured 12.7. 12.5 with the ignition on, 12.2 with the engine switch on and 11.8 at the coil. I'll pull the plugs tomorrow morning to see what they look like.

On a sad note, I dropped the tank during my work and put the first dent into it. The paint it pretty crummy anyway, but I'm still mad that I had an unblemished tank that now has a dent.....

Measured the battery this morning. It measured 12.5.
I pulled two plugs. #1 was brownish. #4 was black.

Here's a selection of thoughts I have:

Should I go back to 3 ohm coils? (I bought 5 ohm because dyna says they are for street use.)
I was also convinced that 5 ohm coils would be easier on the charging system. I have Dyna S ignition.
Certainly my stock 15 pilots can't be too rich. Is it possible my mains are rich, and putting carbon on the plugs at high rpms?

Sorry for wandering between carbs and ignition.