KZ400 w/36mm Carbs... Jetting suggestions?

Greetings all! Searched but can't find any information. I'm a fairly new member so bear with me if I missed a previous post

Long story short I'm running a '79 KZ400 motor on my '81 440 LTD until I can get the 440 motor rebuilt. I've only got the 440's electronic ignition and 36mm carbs since the 400 came with neither. Both fit fine on the 400. I'm using the stock airbox but the P/O installed a 2-into-1 muffler (to my knowledge the carb jetting is stock though). I've rebuilt the carbs and synced/tuned them, Been running it with this setup for a year or so and it's good enough to get around town.

Here's the problem... The 440 motor crapped out shortly after I got the bike so I'm not REALLY sure how it oughtta be performing with either motor (I'm not convinced there'd be much difference). With the 400 it runs smoothly up to 2/3 throttle, then hiccups/misses once it feels like I'm mildly pushing the motor. Feels like it's got more umph hidden in there somewhere, but likewise it feels like pushing it would be...well...pushing it. Not a huge problem around town but in 5th/6th it's a struggle to keep it at 65mph on anything other than level ground. Missing is prevailant above 6000rpms in 5th/6th gear on level ground, and in lower gears under load. I don't run the bike past around 7500rpms even under slower accelleration since it's old and I don't wanna blow the motor, Passing anywhere above 50mph is not an option.

Gonna be a while before I can get my 440 motor rebuilt so here's the questions...

• Would it be worth it to try and re-jet the carbs for the 400 motor? If so, any ideas which jets to try?
• Would I be better off just sourcing the 32mm carbs that came stock on the 400 motor (and the throttle & deceleration cable)?
• Could the electronic ignition somehow be the cause of the missing? Seems odd that it would but hell I'm an amateur,
• Despite the top-end loss (like I'd miss it), would a 50-T sprocket instead of 45-T solve the problem?

Grateful for any pointers.

Edit: FWIW the valve clearance is set to spec for the 400. The plugs have been gapped correctly for the 400, and coil/wires have been replaced with NOS Kawasaki parts (they're the same for both the 400 and the 440).

I'm interested in what others opinion are here but here's what I would do if it were me. If I planned or were forced to run the KZ400 engine for a while then I'd probably try to find a set of correct carbs for it. If I felt that it was going to just be a temporary solution then I'd bear through it and try some rejetting with the current setup. Your plugs ought to tell you if it is running rich or lean. It sounds like it is fine on idle and lower end of the throttle but is definitely too lean or rich on the top end. I'd assume that since it's a bigger carb for a larger engine that it would be too rich on the top end but it sounds to me like it is too lean. Throttle chops will tell you for sure but others with more experience may have better advice for you.

And I don't think it is the electronic ignition - I run the later 440s electronic ignition on my 76 KZ400 just fine. Though it could be a bad coil?

BTW, you didn't mention what is wrong with your 440 but since you have a later 400 engine the bottom ends are essentially the same. You can run your 440s top end pieces on the 400 (jugs, head, pistons). Depending on their condition it might be quicker/easier to do that than troubleshoot and rebuild the 440.

Best of luck to you, I'll definitely be following along.

Well FWIW I did a couple of things that helped.

Discovered "spark leak" lacking a better term. Spark on the outside of the plug between the boot and the metal? IDK WTF you call it. Discovered it the other week when the bike crapped out in the pouring rain. New plugs, wires and boots fixed it... Doesn't cough quite as much at highway speed.

Changed to a 50-tooth rear sprocket (and new chain). Definately gave it some nuts on the hills and passing is far easier around town. Can accelerate in 6th where I couldn't before. Top speed took a noticeable hit though, runs about 73mph at 7400rpm (which is about as hard as I wanna push the motor). Also find myself in 6th more often than I'd like around town to keep the RPMs a little lower.

Old plugs look like it's running rich. Gonna fiddle with it this week.

Do the thumb test on the carbs. Bad or stiff diaphragms can do this.
Steve

swest wrote: Do the thumb test on the carbs. Bad or stiff diaphragms can do this.
Steve

Steve, can you please explain the thumb test in detail?

Randombeat wrote: Steve, can you please explain the thumb test in detail?

Second that. And now that you mentioned the diaphragms I replaced them when I originally bought the bike (both were torn and patched with some black rubber crap). It's unlikely they're bad and as I recall I was EXTREMELY CAREFUL not to screw with the needles since I was fully aware I had no idea WTF I was doing. BUT... likewise, I have no idea if they were adjusted properly to in the first place or if they're set correctly now.

So if there's an adjustment to be made on the needles (and it would make a difference), can anybody point me to a guide for adjusting them properly?

Some needles have circlips that adjust in usually one of 4-5 slots, I believe. You raise or lower he needle to fine tune the carbs I believe, so it would be one o the latter adjustments made, once the carbs are dialed in. My needles don't have them, so I've never needed to research it. But maybe try searching "needle clip position" ?

Sounds like it's lean to me, and the fact that it has an aftermarket exhaust on it would make it go lean too. Try raising the slide needles one notch, or lower the clips is what you will actually be doing. Then try going two main jets sizes larger, that might get it close to being good.

The 36mm carbs will work on a 400.
First get a repair manual for a 440.
Either paper or PDF, factory or Clymer/Haynes.
The stock needles on your carbs do not have grooves.
They can be shimmed up.
Check out Sigma 6 to see if the have a jet kit for a 440.
I've used them before and they are as good as DynoJet etc. .


.

The thumb test is where you hold the slide up with your finger, put your thumb over the large opening, (vent) top back of the carb, let the slide come down to see if it drops quickly or slow. Also to see if it is sticking. Quick (shot) or misinstalled.
Steve

Old thread but wanted to update on this for anyone interested.

Rebuilt the carbs this weekend and indeed the diaphragms were faulty. Surprised me since I had just replaced them in spring '14 and figured I'd have gotten a little more life out of them. Needs sync/mixture fine tuning but it runs a helluva lot better now. Gonna keep that bigger sprocket on it though

Thanks for everyone that assisted!

Interesting that the diaphragms only lasted that long, wonder if the ethanol content in modern fuels has anything to do with this?