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Discussion Starter · #1 ·
OK guys here's the deal. I feel I'm running into a bad lean condition. I did a plug read the other night when I had a main jet clog up on me and they are all white to seeing evidence of detonation. I know not good. So here it goes. My bike 89 zx7, bone stock engine, larger carbs 38mm vs. stock at 36mm. Muzzy header, Yosh mid pipe and slip on from a GSXR750. Clean air and float bowl mod. Stock jets are 112's for federal emissions, and 118's for cali emissions. I have 122's with FP springs, needles, and the clip on the second spot from the top. Now I believe my bike has a cali tank which point to it being a cali bike, but the evap is gone. All of my intakes are air tight, no leaks. Carbs a sealed up real nice. Floats are 15mm where stock is 16mm. Pilots are 38 jets at 2.5 turns and I know thats a little rich as she puffs with the choke and you can smell it when shes warm. And you have to open the throttle a little to get her to start. Now my mid is great. Cold and warm, but anything past 7k RPM at anything over half throttle when shes been running in traffic for a while she just runs flat.

So heres the comp.
Stock mains are 118 for smog bikes. I have 122's.
Slide needles are FP and second from the top no shim
Pilots are 2.5 turns and 38 jets.
Muzzy header
Yosh GSXR750 mid and slip on
Spark plugs are white with some signs of detonation.
Now when I got the bike there were 127 mains in her. I never ran the bike as she needed an engine, and the carbs were so gummed up I had to use jet drills to clear them. Do you think I should go back to the 127's or bigger?
I run at sea level so..
 

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OK, I'll try.
Sounds like you're running lean if it's white plugs and running flat after 7k rpm so I assume you're talking WOT. that would be main jets. I would definately try the larger jets.
If you have the 127s, start there. I wouldn't try bigger only to figure out the 127s will work.
 

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OK I know I asked this before in another one of your threads, but are the 122s stock for 36mm carbs or for the 38mm carbs?
 

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Discussion Starter · #7 ·
Riley I have no idea. I know either way you look at it, would 2mm larger really require that much more fuel? I mean it's a 10% increase.. Now I know some of the guys here are running jets like 180's and stuff but what are the mods? stock? slip on? what are the carb sizes? I'm just at a loss. I'd really like to keep the bike as is, but if I really need that more fuel then wow.. I guess I'll try the 127's and see where that goes..
 

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Riley I have no idea. I know either way you look at it, would 2mm larger really require that much more fuel? I mean it's a 10% increase.. Now I know some of the guys here are running jets like 180's and stuff but what are the mods? stock? slip on? what are the carb sizes? I'm just at a loss. I'd really like to keep the bike as is, but if I really need that more fuel then wow.. I guess I'll try the 127's and see where that goes..
told you.:nana
 

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Riley I have no idea. I know either way you look at it, would 2mm larger really require that much more fuel? I mean it's a 10% increase.. Now I know some of the guys here are running jets like 180's and stuff but what are the mods? stock? slip on? what are the carb sizes? I'm just at a loss. I'd really like to keep the bike as is, but if I really need that more fuel then wow.. I guess I'll try the 127's and see where that goes..
118 main X 10% = 11.8 or 129.8 main jet.
maybe 127 is too small.:dunno
 

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Well there really is more to it than the 2mm diffence in bore. Differences in air bleeds for instance can create a big difference in jet sizes. Do you know what the carbs are originally off of? If you do I wouldn't think it would be hard to figure out what jets came in it.

And by the way I am going to agree it could certainly be lean. Mine would fall kinda flat at about 8grand because of a badly installed jet kit with the main jets way too small. Now when it gets to 8 grand I gotta back out of it because it starts picking up the front wheel:crazyloco
 

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Discussion Starter · #11 ·
Well there really is more to it than the 2mm diffence in bore. Differences in air bleeds for instance can create a big difference in jet sizes. Do you know what the carbs are originally off of? If you do I wouldn't think it would be hard to figure out what jets came in it.

And by the way I am going to agree it could certainly be lean. Mine would fall kinda flat at about 8grand because of a badly installed jet kit with the main jets way too small. Now when it gets to 8 grand I gotta back out of it because otherwise it would wheelie over:crazyloco
Thats exactly what its doing.. When shes cold life is good. After sitting traffic for 30 minutes i'd be lucky to get past 8 grand, but anything before that it's hold on baby. I'm guessing the carbs came off either a 90 or 91 bike. Before they changed to the over the engine air box I would assume.
 

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you asked for brains
limited selection here.
Kinda kills it for us half-wit sport bike riders, doesn't it? Begs the question: If you answer, you profess to be or think you're a brain. :lol
 

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..If you answer, you profess to be or think you're a brain. :lol


Yep, and that almost scared me off:tard

Only thing that made me post up anyways, was the hope that I would accidently say something that would help.
 

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You're more often right than I am, so that makes you the de facto brains here.
 

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Discussion Starter · #15 ·
Well so far you guys are confirming my theories so you are all right. Thanks guys. Just didn't want to tear into the carbs again.. It's getting old.
 

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Oh no, I'm not of the same mindset as any of you, but I'm waiting for you to come back to say 127s made it worse. Then I'll commit. :evil Riley's air bleed size thing could have merit. But it's so hard to tell when you're aren't starting with stock carbs.
 

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I agree only trying something different is gonna tell you which way to go. I say make it a fairly sizable step so that it will give noticable results and then fine tune from there. I think I know where E1 is going. I think he is taking some of the conflicting things in your description and saying it could also be rich. That is, when your saying it runs good cold, E1 is taking that to mean it is too rich and he may well be right. But I think if it is running rich, it is only doing so in the lower end of things and as we know you need the right main jet first and then fine tune the lower throttle stuff with needle height, pilot jet and pilot screw setting after.
So be ready for it to possibly run worse on the slow side with a bigger main jet. I suggest trying the 127s and then get it out and try the top end, ignoring what happens at idle and slow speed at first, just see if the power increases above 8 grand. Then come back and try to reset the rest. Of course I am only guessing too, and only trying something different is going to tell.

One more thing, if you are going to try the 127s, please be as sure as you can that they are really clean and in good shape. You mentioned before having to use bits to clean some stuff. If you scratch the inside of the jets, you cant really trust it to act like a 127 anymore.

Good luck and definately report back:thumbup
 

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Discussion Starter · #18 ·
Yeah the pilot jets are what was really clogged up. I have a clutch pack that is burned up due to having to start it at 6k off the mains with the 127's. I guess I should have left them in there... Oh well.
 

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Went to the 127's and a vast improvement. Still room for more though
So you gonna try bigger? I think I would, even though I totally understand how tired you must be of pulling it apart.
I was just reading up a little on the 7s and it looks like they went to the 38mm carbs in '99, does that sound right? Reason I ask is I read a couple threads where they are running 150 jets and bigger for the '99 and newer bikes with 38mm carbs.
Sorry I cant actually be of more help. I was kinda hoping that someone who has tuned a set of 38mm carbs for an older 7 would chime in. Seems like it would be a fairly common upgrade:dunno
 
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