TOPIC:

I've got a question about the main jets on my KZ440.

First off I think I've narrowed down the part numbers I need to get for the jets:
The primary main jet is 99101-124 (99101-ZF5)
The secondary main jet is 99101-393

According to the service manuals and what I've seen online you should tune for high RPMs and work your way down. So I'm ignoring the issue where the bike doesn't want to idle until it's warmed up for 10 minutes and then afterwards it idles fairly high. If I turn down the idle screw when it's warm then I just have to turn it back up next time I use the bike.

At the high end RPMs the bike is running great except in sixth gear around 60-65mph. The bike is fine going faster but if I let off the throttle to slow down to 65mph it stops pulling or responding to the throttle. If I let the throttle off a bit and then roll it back up it seems OK, but it takes a second or two to go back to regular performance.

I have non-stock airbox and emgo shorty reverse cone mufflers, so everything I've read says this is going to be too lean with stock jets, but my plugs show normal on one side and rich on the other. If one plug is not getting enough air I can see how this could be causing bog down. So I'm kinda lost.

How can I tell if this is due to too rich or too lean?

I have a similar setup with intake and exhaust (cone filters, silicone intake tubes, Emgo shorties)... Have you had the carbs apart and every passage and jet cleaned out thoroughly? Sounds like your pilot jet may be clogged/dirty causing the idle issue when cold and coming off throttle.

If you're rich on one side, you may have to drill out the air screw blockoff so you can adjust the screw on the one side. You'll have to pull the carbs to do this. It's on the intake side, on the top of the carb. Check out this link for some help:



Tim

Found your other thread in the Engine section... Sounds like you went through the carbs pretty thoroughly... And I assume this problem is gone after all the work spelled out in the other thread?

Hey thanks for the help. The other thread was before this one lol. I've soaked the carbs in pine Sol and blown air through everything except the air mixture screw (I forgot to hit that one when I had the carbs off) Everything looks super clean. I got the carb rebuild kit and put in all the new rubber and mixture screws and readjusted the floats for the new needles. I still get the same problem. Bike seems great and is fun to ride around town on but on the highway it still does this bogging thing around 60.

I've played around with the idle screws, they are both at 2 3/4 turns out. Following the manuals instructions this is where the best idle is.

I had an oil leak on the left side which is gone now that I replaced the valve seals. I guess it had been like that for a while before I got it, there was a lot of oil gunk built up on the spark plug wire. I cleaned that up and was hoping for the best but still no difference.

Could a faulty coil give me bad spark on one side? The spark looks the same but it seems pretty subjective...

So I went ahead and ordered a new coil just so I can rule that out.

I feel like I can't start tuning the carb until I sort out the sooty spark plug. I've cleaned the carb and serviced everything as best I can, so both sides should be working the same. I'm not sure how you can find out if there is a piece of gunk in one of those tiny holes in the carb body though, that might be screwing up one side. Maybe another go at it with that carb cleaner spray is worth a shot.

Have you checked the fuel service level in the carbs ?
Page 154 in the KZ440 service manual
To high fuel level will make a cylinder rich. To low will make it lean

Yep, I did check it. After the carb kit I had to reset the float height and I did double check with a clear tube, it is 4mm below the seam on both sides.

Have you checked your advancer to make sure it's not sticking? Coil may also be it. I'm going to stick w/the advancer for now as you've gone through everything else that would most likely be the culprit.

Hey VWRabbit.
I sorted it this weekend. I checked the advancer already, and while I was waiting for the new coil I figured I'd try that spray carb cleaner on the carbs as I had only done the Pine Sol dip and maybe that hadn't dislodged something in one of the passageways. And it turns out that was the culprit, the bike is running great now!

I am really happy to get it working so well with the stock jets and without the original airbox, as I heard that was near impossible. Thanks for the help