KZ440 bogs on hard acceleration and full throttle

It is possible, and even common, to have slightly different mixtures in each cylinder, that is why each carb is individually adjustable. When you had the carbs apart, did you check to be sure that both carbs had exactly the same jets and needles? Some previous owner may have mixed in some different ones. Ideally, each carb should have the exact same jets and needles, and the fine tuning taken care of by the various adjustments.

In the first post you mentioned shimming the pin (you meant needle, yes?) and blocking the air flow, and both resulted in worsening the problem. Have you tried lowering the needle?

riturbo wrote: Have you checked the float height on the carbs ? Search clear tube method on here .

This might help with your tuning www.factorypro.com/tech/tech_tuning_proc...igh_rpm_engines.html

Yep I checked the float height and that seemed OK. Thanks a ton for the link, I think that's going to be super helpful going forward.

TexasKZ wrote: When you had the carbs apart, did you check to be sure that both carbs had exactly the same jets and needles?

In the first post you mentioned shimming the pin (you meant needle, yes?) and blocking the air flow, and both resulted in worsening the problem. Have you tried lowering the needle?

I didn't check the jets, but the previous owner was definitely in the carbs. Yes I meant the needle, I'm not sure how you can lower the needle.

I food it for a long ride and I think I am getting close. Once up to highway speeds the problem becomes easy to reproduce. It really wants to go at full throttle now and I only get the hesitation when the throttle is around 1/2 throttle. So as I accelerate it will hesitate but if I keep opening the throttle it eventually takes off. Then when I let off the throttle as it gets low it hesitates again until inlet it mostly off.

I guess the next logical step is to tinker with jet sizes. From what I've read it's the primary jet that works at around 1/2 throttle so thats where I should start, right?

At mid-throttle, the needle is primarily responsible for mixture.
Low rpm - pilot circuit
Mid rpm - needle
High rpm - main jet
Yes they overlap.

I wonder if you have incorrect needles or maybe two different ones? Oddly, what yo describes is symptomatic of a seriously lean condition, which raising the needles should have helped.

So if it is in the mid-range, then the jet needle/needle jet are the culprits? Or could I just need a larger secondary main jet?

How do I know what the part numbers are for these components? I found this: www.keihin-na.com/assets/1/7/jetlist.pdf

But I'm not sure what to order if I wanted to get new needles, shims for the needle, or different sized main/secondary jets. I couldn't find it in the shop manual either.

The factory service manual should have the stock setup listed. As a last resort, you could open up the carbs and look for the numbers stamped on the jets. Yes, they can be really hard to see.

I took apart the carbs again to take pics and look for anything that could be wrong.

The jets are stock sizes. I noticed the floats had different numbers on them, not sure if that means anything. I attached pictures of the two spark plugs.

I noticed the little plastic plugs for the pilot jet weren't sitting snug in their holes and the rubber was quite worn so I put some aviation form a gasket on them because I read that this was resistant to gas and now the bike runs great!

Good deal. I am glad it turned out to be a cheap and easy fix.

Yes, thanks for all the help!

It still bogs down a tiny bit, but it is way better than it was before. It won't bog down while accelerating anymore, only when I let off the throttle at highway speeds. When it did that before it was a bitch to get it to "unbog" but now I just let go a bit and as soon as I add throttle it goes away.

I think I'll get the carb kit and a couple of different jets and see if I can get it running perfect but for now it is 99% and I'm really happy to take a break from obsession over this

Gas resistant gasket maker usually means resistant rather than gas proof so your problem may come back. If so then measure the plug groove and get some Keihin o rings from Z1 Enterprises. Been there done that Just cant remember the size. Nessism may have that info.
Great that you found the problem .

Thanks for the tip, I did order the carb kits which come with new rubber so this fix only has to last a week

Well I fixed it finally. The carb kit seemed to help a little bit, i had to readjust the float height, but it didn't fix the problem.

What did fix it was me taking apart the carbs again and instead of pine sol dip this time I got some spray carb cleaner and hit every hole, surface, jet, etc. with the carb cleaner. Then I did it again. Then I did it one more time for good measure.

I guess there was something in one of those passageways that the pine sol dip didn't sort out, but the carb cleaner got it. Now the bike is amazing. I've been on two one hour rides with it now. The first ride it did the bog down once for like 2 seconds, and the second ride it didn't do it at all. And this was with me trying to make it do it on the highway where it would do it all the time before. So I am 100% confident now it is fixed! Thanks everyone for all the helpful tips!

I feel kind of silly now but at least it's sorted!