82 1000 LTD Upper RPM Breakup

Greetings:

I'm throwing my 1st official post out there for what hopefully will be some collective wisdom.

It's been 35 years between KZs and I'm excited to get this one going. There is 1 problem I can't seem to properly diagnose.

She starts and idles perfectly and pulls hard right up to 4000 rpms and then begins to stumble and miss above that. You can go WOT to 4K, or attempt to baby it up there, just barely cracking the throttle. Either way, the same result, once you hit that 4K mark, the same stumble happens regardless of throttle position.

Here's everything I've tried so far.

Complete Carb Overhaul
New coils/wires
New plug
New ignition (old one was broken and wasn't getting 12V to the coils)
Checked mechanical timing advance for function
Checked plug boot resistance
Cleaned the kill switch

The only thing that didn't seem right was the resistance of the ignition pickups. When I check the pickups, the resistance starts at around 1,700 ohms and slowly (like over 30 seconds) drops just below 600. That doesn't seem like normal behavior, but it's not a cheap part, so I hate to just keep throwing parts at it.

If anyone has any suggestions, I'd like to hear from you.

Thanks

What spark plugs, plug wires, and plug caps are you using?

Does it affect all 4 cylinders at the same time?
What comprised your new ignition swap?

The plugs are BR8ES
The Caps are Nichiwa LB05F and XD05F
The coil wires came with the coils that the previous owner put on the day before I got there (I'm told, they appear new). There's no part number on it (see photo)

You have resistance spark plugs and caps which is not recommended. if you also have resistor plug wires you could end up with a really weak spark that is being blown out at higher RPM.

only 1 of the components should be resistor: plugs, caps, or wires.

switch to standard spark plugs and see if that makes a difference

It may not be the source of the problem, but I would question why one would use resistor spark plugs and resistor caps. Ed

As above.
You should only have one source of resistance so need to change plugs or caps for non resistor type.
There is a very good chance that this is your problem.

That makes sense,

I just replaced what was in it, I'll pitch some B8ES plugs in it and update the Topic.

Thanks gents
Scott

Sorry F64, I wasn't clear on the Ignition swap, I changed out the ignition switch, not any ignition components.

I put the non-resistor plugs in it, and though it seems to run better, I still have the breakup.

There's something just not right with it.

Starts and idles perfectly, but even cruising along slowly at 2K rpms, I hear this random "pop back" ta.........ta.ta........ta........ta.ta.ta.......ta...t.a I just don't remember my old one doing that. That clears up under light acceleration and again, pulls nicely and smoothly to 4K, then falls apart.

I also took it up to 4K and opened the choke 1/2 way to see if it perhaps it was starving for fuel, but no difference.

Voltage at the battery at idle is 12.8 volts and at 5K rpm is 14V

Still searching.....

Can you post a pic of the old spark plugs, showing the electrodes?
Regarding the carburetors, what size are the pilot and main jets, and are all slide diaphragms intact?

Dave,

Attached is a pic of the new plugs after a brief run up the street after install (less than 5 miles).

It for sure seems like #1 and #4 are not happy!

The jets are stock (127) and I checked the diaphragms to ensure they worked when I had them apart.

Those pics are giving every indication of a fuel problem.
Synchronise the carbs with gauges if you have them or can borrow them, if not remove the carbs and using thin paper, cigarette paper works, place the paper under the throttle butterfly and using the throttle screw and the carb adjusters on the throttle rail adjust until the paper begins to slide at the same time in each carb.
When the carbs were refurbished did you have new diaphragms installed,even if you did check each diaphragm by holding it up to a light source.
If any light is coming through the diaphragm, anywhere dry it and then apply a thin layer of flexible silicone sealant, petrol and ethanol resistant sealant is commonly available, over the hole and reassemble after an hour or two to see if there is any change.
If there are no holes or cracks in the diaphragms check you have adequate fuel flow by running about half a pint into a container straight from the tank, I once had a mystery loss of power that was a blasting bead. The bead floated in the pipe until it was drawing enough fuel to pull it down and constrict the pipe where it attached to the carbs.
If this doesn't sort it buy some transparent tube that will push onto the float bowl drains cut into 9" lengths and run it back up into the rack then, with the fuel feed open on prime and the rack straight and level open the drain screws. This will indicate accurately the actual amount of fuel in each float bowl.
These simple checks should find most common issues.
#Good luck