Tuning with an o2 sensor, advice/tips?

Yeah, the problem I found is that since you are getting hard numbers, you are willing to spend way more time on fiddling with settings. Before you would get close and that was that. Now I'm actually adjusting the needle in tenths of a clip just to see the differences. You have to sync the carbs everytime too.

Hopefully it'll get easier to make a first guess and get it right now that I have some test data to go by. I'm also getting much faster at making jetting changes.

Here's a tip: in 15 years of cleaning carbs and rejetting, I have never replaced a bowl gasket. I just spread a super thin layer of antiseize (silver) on the gasket and it comes off like new everytime. Also use it on the bolts, of course.

By the way, the plugs look good other than #3 being different. But they are not showing the WOT condition. Plugs take time to show the differences and you just can't spend much time at WOT. They are mostly showing the cruising range (or idle range) which seem ok on your bike.

Plug chops really only tell you when you are way off. When you are close, the plugs always look pretty good. Even Dynojet says the plugs are not really a good indicator.

At the end of last year I checked the float height with kawasaki's nifty tool. they all looked a bit high. This year I have been noticing after every ride fuel in the overflow tubes. So about 4 days ago I dropped all the floats slightly.

I have not re-checked the fuel level as my nifty tool is missing. I have been looking for it on and off. Once found I will re-check the level.

the #3 float did seem to be slightly tweaked, so there may be a higher fuel lever in that carb, but I have not noticed fuel from the overflow tube since the adjustment.

Those plugs also have about 1,000 miles on them; so the color could have been from before I dropped the level.


Choke plungers: there is no noticeable difference in idle when I wiggle the choke lever so I assume the plungers are still good.

valve lash was checked and set less than 2,000 miles ago (although there is a tick as if one is slightly to large.... I need to check again).

Compression test showed all cylinders to be within about 8% and leak-down was done, my mechanic buddy checked both for me mid last season and told me the motor was tight. I trust him so I trust those results.

the mixture screws... those buggers have always made me wonder. I can not hear any difference in idle no matter where I set them from 1/2 turn out from seated till 3 turns out. The only time the idle changes is if i shut the screw... but they all look physically ok... If you think it would be worthwhile I I could change them out (if replacements can be found!)

Sounds like you have covered most of the obvious variables. I agree, put more miles on and check the plugs again. Maybe even swap plugs around, but keep track of what went where. If #3 still comes out as the odd one, then you'll have to look closer at everything on cylinder #3.

Coincidently, I had a similar issue with my #3 plug being noticeably leaner. In my case it was indeed the float level (by about 5mm). I may have knocked the floats and changed the setting on one of my jetting changes.

Next time you have the carbs off, make sure the slides only get to the top of the carb bore and don't go past that point. That will produce a richer reading at WOT than the jets are producing. (That's because opening the slide past the top of the carb bore makes the needle allow more gas, but no extra air gets in. As you go past the top of the carb bore, all you do is add fuel. This can make the AFR plummet rich even if the mains are lean.

Hey guys I just want to say thank you for everyone helping me on this! You folks are awesome.

I have some pic's to post tonight... I am still getting fuel out of the overflows so I need to check float level to see if the float needles need replacing or if it is just still to high.

I put in 125 mains and dropped the needle (it was in the #2 from top position, now it is in the #4 from top position). The bike runs great. I am getting 13-13.8 at WOT, midrange is right around 13.5-14.8 the only real problem spot is at about 10% throttle I am seeing 10's-11's which is a bit rich so I may drop a pilot jet after all.


I need more time actually watching the o2 gauge I was having so much fun riding I did not pay enough attention to really see if changes need to be made.

As far as I am concerned I got better results with one adjustment using this o2 sensor than than I would have with months of trial and error (plug chops and that kind of voodoo!)

If you are seeing 10's and 11's while opening the throttle (in the 10% range) from idle, then that's normal.

If you hold the throttle at that position, it should eventually lean out into the 12's, 13's, or 14's as the RPMs go up.

no I am seeing the 10's when I am crusing with a slightly cracked throttle at speed holding it there... I have watched it on and off for about 10 seconds at a time before riding conditions or personal enjoyment caused me to whack the throttle.


I cannot believe how much more responsive the throttle is. Not a feeling of more power more like power on demand. It is nice.

The current issue:

notice all the fuel in the overflow tubes:

Here is a close up of one of one of the float needles... I think they may be shot but I want to check the float levels before I but replacements.

one other pic just for giggles... this is the future of the bike I still need to do a lot of grinding to get rid of un-needed bits and of course actually get working on the swinger but yeah it's on the back burner.

I should have mentioned, needle changes can make a huge difference. That would explain the big difference in the 10% range. I would try the third clip before changing the pilot jets. If that gets you into the 12's or 13's (at 10%), then I'd stick with that and adjust the mains to get the WOT right.


I think you may be at the point where you are going to need a more precise throttle position indicator. It's easy to do, just cobble up something like this. It's easier to do fractions since it's easier to eyeball where to make the marks.

I set the zero mark where the throttle just starts to raise the RPMs in neutral. The WOT mark is wherever it stops at, (making sure your slide stops flush and doesn't go above WOT).