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Discussion Starter #1
OK guys you all know what I have been doing with my bike. Mainly carb jetting is my issue now. Everything is clean, main jets are 126's across the board, FP jet needles, number unknown. The needles are set on the third from the top and I can't for the life of me figure out why according to O2 AFR gauge it read lean at 8K RPM at full throttle, after cruising with a friend of mine for a couple of hours in traffic.. First start up and with a cold engine I can break the rear tire loose and drift the bike if I wanted to. After warmed up to about half on the gauge and burning my legs on the frame, Shes a little rich in the mid but pulls great to redline. It's something to do with the heat generated while sitting in traffic.. Could it be I am chasing a carb ghost and need to look at ignition?

Let me break it down and hopefully one of you carb gurus can help

89 ZX7 H1
Stock engine and airbox/airfilter
Muzzy header
Yosh RS3 mid pipe and slip on from a 05 GSXR 750
38mm CVK (36mm was stock)
Main jets are 126's
Slide needles are third from the top
Floats are at roughly 15mm...
 

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How did you jet the bike? Did you do any plug readings?
 

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OK guys you all know what I have been doing with my bike. Mainly carb jetting is my issue now. Everything is clean, main jets are 126's across the board, FP jet needles, number unknown. The needles are set on the third from the top and I can't for the life of me figure out why according to O2 AFR gauge it read lean at 8K RPM at full throttle, after cruising with a friend of mine for a couple of hours in traffic.. First start up and with a cold engine I can break the rear tire loose and drift the bike if I wanted to. After warmed up to about half on the gauge and burning my legs on the frame, Shes a little rich in the mid but pulls great to redline. It's something to do with the heat generated while sitting in traffic.. Could it be I am chasing a carb ghost and need to look at ignition?

Let me break it down and hopefully one of you carb gurus can help

89 ZX7 H1
Stock engine and airbox/airfilter
Muzzy header
Yosh RS3 mid pipe and slip on from a 05 GSXR 750
38mm CVK (36mm was stock)
Main jets are 126's
Slide needles are third from the top
Floats are at roughly 15mm...
What does the o2 read at WOT? at idle? at 6,000rpm?How old is the O2 gauge? Is it possibly bad?
 

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Discussion Starter #4
2Fat I was wondering if the sensor was true. At idle it reads 16:1 cruise around 6k it reads 14:1 or so. It sweeps back and fourth. WOT after a good mild cruise, it hangs out at 15:1 which is too damn lean. I need it closer to 13.5:1 at WOT. Now I have an exhaust leak right after the sensor, so that explains the lean idle. At WOT it shouldn't effect the reading that bad. Either way I'm stumped and I dont want to just keep feeding more fuel only to find out it wasn't right. Also the jets that are in the bike now are the same ones I pulled out when I got it and replaced with the stock 112's. The only difference between when I got the bike and now is the lack of my race cams, and I changed it to a yosh pipe and not the Muzzy shorty I got it with.
 

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That is interesting...

Cold start the engine runs like a raped ape which would point to possibly running rich.

As the engine warms up, it begins to run lean, but then you say it is running rich at midrange?

Either way, I would jet for the warm or hot engine even though it seems to run extremely well cold.

I would go up to 128 outer and 132 inner jets and leave the clip and see what the readings are.

Josh
 

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Discussion Starter #6 (Edited)
Also if I were running that rich to give a false lean reading on the O2, then I should be blowing black smoke and It's not. I get a small puff when I romp on the throttle but other than that nothing.

Bullitt, I was thinking the same thing jet it for a hot engine. But, It doesn't seem to make a difference. Now I know that my valves are all a little loose cause I can hear them. But again it's not enough to warrant this jetting issue. As of now after the temp gauge starts to rise a little there is enough power to not only drift the bike, but if I wanted pull the front end up. As long as the temp gauge stays below half life is good. If it's able to hang at half long enough to keep the fan running then its a no go.
 

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Discussion Starter #7
I forgot to mention I have done the clean air mod and float bowl mod to the bike. Not sure if that would make a difference.
 

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Does our valve lash open or close up as the engine warms up?

With regular engines I have built, an all iron engine closes the lash. Aluminum head and iron block opens a little and aluminum head and aluminum block opens a lot.

But with an overhead cam in an aluminum head with iron rockers it makes me wonder. I could see running rich cold and as the engine heats up and the lash OPENS the valves are no longer opening as much coupled with a hotter engine running leaner and now the engine is really running leaner.

Does that make sense?

Josh
 

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Make sure the Kleen air mod isn't causing false readings. If you're sucking fresh air into the exhaust it will show lean.You need to tune it by the spark plugs.Start it and let it idle for 5 minutes without the choke and don't rev it above 1800 rpm. Just let it idle on it's own if it will. shut it off and pull a plug. see what it tells you. If it's lean,then adjust accordingly. Next do the same with the high rpm.
 

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Discussion Starter #10 (Edited)
Bullitt yes it does make sense as it will not allow enough mix to get to the engine and would cause a lean condition. 2fat2fly I have already done this, and at idle I'm nice and tan. in the mid at the moment I'm a little darker. At WOT white and "bubbly" as to warrant detonation. This was with the 112 jets, the 114 jets, and the 122 jets. I have not checked it with the 126 jets yet. Now logic would tell me that if stock was 112 for the non cali model and 118's for the cali model (which my fuel tank is a cali model). Still 118-126 is a decent jump. If anything I should be running rich at this point, but the bike just stops pulling at 8k. This is why I am wondering if I am chasing a fueling ghost and should be looking at ignition, or something else. It's like it hits a brick wall and a friend of mine (who rides a stock 06 katana and is quiet as shit) was following me and said it sounded like my bike just shut off when it does this. Now it did get a little better when I went from the 122's to the 126's according to my AFR gauge. I was at 15.5:1 and now am hitting 15:1 but I should be getting better than that...I guess I'm just going to have to install my wideband to get a better and more accurate read of my afr.
 

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Bullitt yes it does make sense as it will not allow enough mix to get to the engine and would cause a lean condition. 2fat2fly I have already done this, and at idle I'm nice and tan. in the mid at the moment I'm a little darker. At WOT white and "bubbly" as to warrant detonation. This was with the 112 jets, the 114 jets, and the 122 jets. I have not checked it with the 126 jets yet. Now logic would tell me that if stock was 112 for the non cali model and 118's for the cali model (which my fuel tank is a cali model). Still 118-126 is a decent jump. If anything I should be running rich at this point, but the bike just stops pulling at 8k. This is why I am wondering if I am chasing a fueling ghost and should be looking at ignition, or something else. It's like it hits a brick wall and a friend of mine (who rides a stock 06 katana and is quiet as shit) was following me and said it sounded like my bike just shut off when it does this. Now it did get a little better when I went from the 122's to the 126's according to my AFR gauge. I was at 15.5:1 and now am hitting 15:1 but I should be getting better than that...I guess I'm just going to have to install my wideband to get a better and more accurate read of my afr.
Definitely go with the wideband. If i were you I'd try a set of high 130's jets just to see what happens. You're clearly lean and need to address it before you hurt something.You have the idle circuit right. Do not mess with that. Don't touch the mixture screws either. Get the main jets to read right. Do this by changing main jets. I know I'm repeating myself but go higher on the mains. When you have them right then you'll adjust the needles as required (if required at all).You have two of the 3 main pieces of this puzzle figured out. Get the mains and you'll have it mastered.
 

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Good luck young Grasshopper.
 

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Discussion Starter #13
I never put this into the equation but I'm running sea level. I guess that would constitute for a drastic jetting change. I'll see if I can get that wideband sensor out of my neon. A real pain in the ass trying to work around the turbo and minimal room to get my paws in there.
 

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California fuel tank, eh? That reminds me of someone else who plugged the red or the blue vent and ran into issues. Swapped the plug to the other one and the problem was solved. I think it had to do with how the tank vents and equalizes atmosphere inside the tank as fuel load drops. Worth checking or experimenting with.

Or it's possible that the main jet's emulsion tube is limited to how much fuel it can feed or perhaps there's an air bleed at the front of the carb intake that isn't allowing enough air through to take advantage of jets larger than 112/114/118. If that's the case, tuning those carbs is going to be a long road indeed. :banghead

And you can try an experiment that I used to find out if my jetting was right. It's quite simple. Pour in about 1/4 cup 10w40 oil into your air filter (which you can clean out after the test). Evenly distribute, then drain the air filter for about an hour at a 45* angle. Go ride. If it's lean, the reduced airflow will bring a lean mixture back in line and the bike will run beautifully. If it's too rich, despite the O2's reading, the bike will chug and buck at 1/2 - WOT when hot, proving the jet needle is set too low and/or main is too large.

And as always: Factory Pro CV Carb Tuning Procedure.
 

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Discussion Starter #15
Well on the fuel tank I know what you're talking about. I left all the lines open for the vents and only connected the fuel out lines. Now given as how these are 90 model H2 kit carbs, it shouldn't be an issue. I just need to figure what the main jet sizes are for an H2. And in respect to your air jet theory, what if it's backwards in your thinking? maybe it's letting in too much air and not allowing it to pull right. I know the only thing I have changed on the carbs from when I got it was the float height, and the jet sizes. I am now back to original jet sizes so the only thing left is to raise the float height back to 13mm...
 

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Discussion Starter #16
I just remembered something. ya know those O-rings that fit inside the carbs that seal the air box to the carbs? Mine are missing. Now unless I'm over thinking this, could that be the reason why I'm having this issue? Plastic expands and stops sealing properly causing it to not want to rev when it gets hot?
 

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:evil Actually the air bleed at the carb intake idea would be a hypothesis on my part. The oil in the air filter is the theory, as it can be retested and the results verified.

But getting back to the air bleed, I don't see the reverse. That, to me, wouldn't add up in how I interpret air and fuel movement through a carburetor.

You have to come to the conclusion that being at your wits end, you need to find something that you can verify. I don't see that from your results at this point. I see you coming back with readings of 16:1 AFR and such, but the bike runs great this way, but not so great that way. Throw it all out, at least temporarily.

Really. Give the 'oil in the air filter' experiment a try. I'm assuming you have a K&N or BMC and not a paper element unit. Drown that sucker in oil, naturally drain, and ride. Factory Pro says find your main jet first. Take the cold engine and WOT at ~3,500 RPM and record the results. Keep doing the same test as the engine warms over a period of 10-15 minutes of hard use. The results should give you something you can verify. It'll be something like:

1) cold WOT pulls hard to redline, hot not so much or sputters & bucks
2) cold WOT pulls hard to redline, hot pulls better to redline
3) cold WOT pulls hard to 8K then stops, hot same deal
etc...

If the results do not match Factory Pro's theory, then your problem may not or probably isn't jetting related, i.e. float bowl mod issue, vacuum, compression, ignition, etc.

I'm just trying to give you something to go on. Something that will give you a baseline to work from and improve upon.
 

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Brings back fond memories of endles carb tuning with with Holleys on the GTX. Good luck with it. I don't think it's possible to ever get it just right. It's always a compromise. You are quickly becoming an expert now, aren't you?
 

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Discussion Starter #19
All i can say is that everything i know about carbs and airflow is being rejected by these carbs. God I cant wait to get my FI back on the bike.
E1 it's not doing anything that you listed
1) cold WOT pulls hard to redline, hot not so much or sputters & bucks
2) cold WOT pulls hard to redline, hot pulls better to redline
3) cold WOT pulls hard to 8K then stops, hot same deal
etc...
It's more pulls like a litre bike when cold, a little less when warm and then hits a brick wall like a rev limiter when hot. I'll try to get an audio recording or a video made to show guys what its doing.
 

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The CV procedure works very well on these things. You say you have the idle and cruise set, but you have problems at WOT... well, you need to set up the mains, needles, then float height before you screw with the idle circuit.

If your bike is getting worse @ wot as it warms up, then it is too rich. Experiment with smaller jets, spark plugs be damned (buy some extras) until it runs the same hot and cold.

I do not however understand this

At WOT white and "bubbly" as to warrant detonation
"white and bubbly" (ashy) would indicate that it is lean as hell and would be promoting detonation... Perhaps that is what you meant? That would of course be in line with your A/F ratios...

Your plugs are telling a different story than your butt dyno it seems. Do you have the "original" carbs on there, or did you swap something else on?

And, shouldnt you have two different jet sizes in there instead of one size across the board?

Perhaps you have the right size for the outer cylinders, and then the two in the middle are too lean. Or maybe the other way around.

Do you check all four plugs when you look at their color?
 
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