Another KZ-440 Carburetor thread!

Hi all!

I'm at my wits end here. Bought this bike last year rode it around (don't know how that thing even ran), every other time it would run ok and the rest it would cough and hiccup.

Atm it runs fine in the lower reg range when stationary, but as soon as I'm pulling away it starts to miss and hiccup. Full throttle only results in hiccup and eventually dying. But revving it from idle in neutral sounds great.

I started looking into the carbs that had a torn diaphragm among other things and to make a long story short, they have been ultrasound cleaned and fully rebuilt using Keyster kit. Float levels checked and synced. I've probably had them in particles 10 times now.
Also I checked the valves and compression. All fine!

Anyway, put new coil, leads and caps also, points and condenser still not changed though, but spark is fine and starts easily, as is advancer which I'd checked with timing light.

But I'm really at the point of giving up. I've tested it with and without stock airbox and it seems to run "Best" with the cheap pod filters. But plugs are black so it gets too much fuel obviously.

What am I missing?? It such a simple bike and I'm an avid mechanic used to fixing a lot more complex bikes without a problem but this seems to have gotten the best of me! I'm having the same problem now matter what I'm doing it seems so I'm sure there is something I'm overlooking. Please help!

I didn't see a 1980 KZ440-C1 in the diagrams at Partzilla. Is this a Euro model or something? I would make sure the airbox is complete & properly installed >> apparently on some 440 models the airbox cap can be installed wrong, causing a vacuum leak. You'd probably need to go back to the stock jetting & stock carburetor parts. some aftermarket stuff might not work right. Also make sure the airbox ducts & carb holders are good.

Unless I'm missing something, a 440 should have electronic ignition so there won't points to cause problems.

Black plugs could also be the result of burning oil. A small amount might be sneaking past the valve guide seals and/or the rings - not enough to cause obvious blue smoke in the exhaust but enough to darken the plugs.

To Martin's point, it sounds like you have an air leak that is leaning out the jetting, likely at the engine side with the carb boot/holder. As the boots age they become less pliable: removing and reinstalling the carbs and keeping the old boots may have resulted in one or more small cracks which can now let in air.

New boots are inexpensive. You might as well get a new set and see if that eliminates the problem. Don't use an entire tube of silicone like the PO of one of my project bikes did. :sick:

Did you buy it with pods already installed? Maybe someone already altered the jetting for pods.

Did you replace both diaphragms?
I find that they initially tear in places that are not seen easily. You have to inspect the area near the slide really closely.
If the diaphragms are torn, the slide won't open properly and you won't get power under load, but it will rev somewhat in neutral.

Thank you for your points! Jetting is stock, both diaphragms are new, it's an '80 440 with points ignition.

The f-ed up thing is that at one point during searching it ran great! Plugs were perfect color and it pulled cleanly through the rev range. Happy as a fiddle at finding the fault, but the next day it was back to the same old devices. This was with pods and std jetting and is what is mostly playing with my head.

I haven't tried sealing the std airbox with silicone, but that's about it. Lid seems fine though and it has new filter.

Boots seem fine and flexible as does the springs which seems tight.

And if it was lean, the plugs should be white, not black as now unless it's sucking oil as noted. Any far out faults someone has found??

I think I would start looking at the ignition closely before spending too much time on the carbs.

First thing you want to do is verify that the coil has battery voltage on the positive side and that it is steady.

Duly noted. I'll check. Thank you!