1980 kz440 ltd Carbs

Hi, first time poster here. I've got an '80 model 440 ltd (as the title says) that's been having carb problems since I got it. We've taken the carbs off several times and tried adjusting them and cannot get it to run right. The bike will run fine for a while but if you get out on a longer run the RPMs want to surge up at lower speeds. There's also a fine black soot showing up in the tail-pipes which makes it seem like it's getting too much gas. I'm not a huge mechanic but my dad, who's been helping me work on it, says that someone may have rejetted the carbs before (whether accidentally or on purpose) and that could be why it's getting too much fuel. If this is the case we would need a new set of carbs correct?

If anyone could point me in the right direction to shop for new carbs, or give some other ideas of how to fix this problem, I'd really appreciate it.

Thanks.

Welcome to the craziness!

I doubt that you need new carbs. I'd be willing to bet that it's an adjustment problem like floats set too high. The clear tube method is the best way to set them. If the carbs have been re-jetted, that's easy to undo - just put the correct ones back in.
Have you cleaned the carbs REALLY well? There are a bunch of really tiny passages that have to be perfectly clean to function. No amount of adjusting will offset clogged carbs. Did you carefully insped the very delicate diaphragms in each of the carbs? If there is a tear or even a tiny pinhole, the carb will not function properly.

Go to the KZ information section of this site and look for an article called Carbs 101, or something like that. Also spend some time looking in the carb section of this site and don't be bashful about using the search function. Also, get a factory shop manual. It will save you many dollars and much frustration.

There are two articles titled, Carb Cleaning 101 and Carb Cleaning 102. They should set you on the right path, but are not a substitute for a factory shop manual.

I'll read those over and try to make time to remove and clean the carbs again this weekend and update after that. If it is the jets how would I go about getting replacements for them?

Is the stock airbox properly installed?

Jsoden, welcome.
I would suspect the diaphrams.
I just went thru a simalar problem on a 81 440 LTD. High idle (4000 RPM)choke or no choke. 1 diaphram had a hole about 1/8"(3mm for the rest of the civilived world)long.

I repaired it with a small piece of electricel tape on one side and sealed it with a dab of crazy glue.

Starts, idles and runs like a champ.

Hope your solution is something simple.

Good Luck,
Jim

@JMK As far as I know the stock airbox is installed properly but I will go ahead and double check that sunday when I'm out working on it.

@Rainman I have checked the diaphragms and they appear to be in good shape. I hope it turns out to be something simple too though. Thanks for the input.


This is really a learning experience for me working on these things so any and all input is helpful even if it doesn't exactly fix my problem. It helps me remember things for future bikes.

I don't know if this applies to your bike, but here's a simple check for some 440s.
Lift up on the back of the airbox cap - it shouldn't move. If it does move, then it isn't installed correctly. Apparently, it's easy to install the cap wrong.

Note: don't forcefully lift up on the cap. KZ440 airboxes & airbox caps seem kinda rare, so treat them with kid gloves.