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Discussion Starter · #1 ·
Hey Guys,

I recently acquired my first-ever motorcycle, a 2000 ZX7R. It's also my first experience with a carbureted engine (I have rebuilt/tuned fuel injected car engines plenty). I've read a bit on what each setting on the carb does and what throttle ranges it effects but haven't been able to get the tune dialed in as nicely as I would like (engine bogs/dies from running too rich at low RPM uphill).

The bike has:
K&N Filter
Yohi RS-3 Pipe
Float Bowl Mod / Emissions Delete
Factory Pro 182K/172K inner/outer Main Jets, with 100K needle jets
Stock(I think?) 35 pilot jets
Stock(?) N140 needles
Float bowls are all at about 14.9mm
Pilot screws all at 1.75 turns out
Needles shimmed about 0.6mm

I cleaned the carbs and all of the jets are clear, replaced the o-rings on the float bowl needle seats, and everything else looks good. The thing is, since it seems the richest at idle/low rpm then the pilot screws should be set leaner, which means screwed in more, correct? They seem like they are in more than anyone else's I've read about, most people are between 2-2.5 turns out...

Any carb pros have any reccomendations on how to make this tune better? (Hopefully keeping these jets, since they came with the bike and I don't have any other ones.)

BTW - I live in the San Diego area so pretty low altitude.
 

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I think you'll be able to tune the carbs. Sounds like you understand how they work and what you're looking for, based on experience. Tuning them for low & high altitude, like for making runs up to Julian, can be a compromise. Set them for where you'll be doing the majority of your riding.

I'd recommend Factory Pro's CV Carb Tuning Procedure. In it, it clearly sets for the proper way to tune, by starting with the best main jet and working your way down through the fuel circuits. I gander that based on your current main jets, that is the problem. Can't say for certain though. You'll want to ask what other 2000 ZX-7Rs run stock to give you a baseline to compare the FP mains to. Keihin jet numbers are similar to FP, if not exact. And just for comparison, my 9Rs run Keihin #158 - #165 on an engine 150cc larger than yours.
 

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The bike has:
K&N Filter
Yohi RS-3 Pipe
Float Bowl Mod / Emissions Delete
Factory Pro 182K/172K inner/outer Main Jets, with 100K needle jets
Stock(I think?) 35 pilot jets
Stock(?) N140 needles
Float bowls are all at about 14.9mm
Pilot screws all at 1.75 turns out
Needles shimmed about 0.6mm

I cleaned the carbs and all of the jets are clear, replaced the o-rings on the float bowl needle seats, and everything else looks good. The thing is, since it seems the richest at idle/low rpm then the pilot screws should be set leaner, which means screwed in more, correct? They seem like they are in more than anyone else's I've read about, most people are between 2-2.5 turns out...

Any carb pros have any recommendations on how to make this tune better?
Most of your settings look good. Float height setting sounds a bit lean but some people have had decent results with a 15mm setting so I wouldn't worry about it.

I think you're on the right track with the pilot screw settings. Try 2 to 2.25 turns out (from fully seated). That range seems to yield very good if not ideal results in a pilot screw setting from my experience and that of others. You may have to go as far as 2.5 turns out but I doubt it.

My bike is set up very similar to yours. My specs and settings:

K&N air filter
Full Muzzy exhaust
Float bowl mod
Factory Pro stage 1 jet kit
Main jets - 182/172
Pilot jets - #38 (one size over stock)
Float height - 14mm
Pilot screw setting - 2 turns out



Hope this helps.
 

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Discussion Starter · #5 ·
If I turn the pilot screws out more, won't that richen it further? I think it's already quite rich, since when I try to make it up the super steep road to my house, the RPM's will drop down and the engine will bog and die. It smells like unburnt gas then, so I think it's too rich. Unless I've got it backwards and in is richer, out is leaner?

I was going to remove the needle shim and turn it in another 1/4 turn to 1.5 turns out and see if that helped any...
 

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Yes turning it out will richen. I'm in Toronto which is on average ~ 200ft higher than San Diego but we're both near water (great lakes in my case, Pacific ocean in yours). My settings are:

K&N filter
Full Hindle
Float bowl mod
Factory pro vacuum slide springs
Main jets - 178/168
Pilot jets - 36
Pilot screw settings - 2/2.5 turns out
Float height - 15.5mm
Stock needle with no shims

Usually after doing the float bowl mod/emmissions delete 7Rs run a tad rich. My Factory Pro kit only came with jets that were smaller than stock so I'm surprised you have bigger jets... but then again your closer to sea level.
 

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Discussion Starter · #7 ·
I'll try the following then:

Increase float height from 14.9mm to 15.5mm
Remove the shim on each needle

If that doesn't lean it out enough, I will screw the pilot screws in from 1.75 turns out to 1.5 turns out.

What is the most the pilot screw should be turned in before the mains have to be swapped down a size, 1 turn out from bottom?
 

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Before running off and making any carb changes I would start with a good sync. THen if you still decide you need to make some changes make sure to sync again before testing.
 

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Discussion Starter · #10 ·
Oh, I thought the order was:

Check valve clearances and shim as needed.
Make sure there are no intake/vacuum/fuel leaks.
Tune carbs (jets, needles, pilot screws).
Sync carbs.

I was under the impression that syncing the carbs is the last step because any changes to anything else can throw the sync off. Or is that true, but you also need to sync them after every tuning step before testing each tune?
 

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Oh, I thought the order was:

Check valve clearances and shim as needed.
Make sure there are no intake/vacuum/fuel leaks.
Tune carbs (jets, needles, pilot screws).
Sync carbs.

I was under the impression that syncing the carbs is the last step because any changes to anything else can throw the sync off. Or is that true, but you also need to sync them after every tuning step before testing each tune?
If you have to pay to have someone sync then you are 100% absolutely positively correct without a doubt. However, if you have a sync tool, like a Carbtune or MotionPro, performing a sync before and after can only help. It won't be the source or solution for a rich fuel condition though.

I get the impression you're making a procedure list so you tune once and you're done. Good luck with that. I'd lower my expectations and knock one thing off at a time, roll with the punches and look at successfully solving your bike's woes in an expeditious fashion as a bonus rather than a necessity.
 

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Discussion Starter · #12 ·
I get the impression you're making a procedure list so you tune once and you're done. Good luck with that. I'd lower my expectations and knock one thing off at a time, roll with the punches and look at successfully solving your bike's woes in an expeditious fashion as a bonus rather than a necessity.
I just didn't know syncing it so often was helpful, I thought it was simply the last step. I already took the carbs off my bike and reassembled it 5 times, so what's another few times? I will do this in as many steps as required to do it right and get the best results, so just let me know :smile

Anyways, now that I know I will be needing to sync the carbs often, I cooked up a little something:




Now all I need is a carb adapter set (those brass tubes to screw into the holes under the carbs, where the carb sync tool hoses will attach).

What size carb adapter tubes do I need?
 

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may be a stupid question but are you sure its the carbs causing the bogging down?
when i got my zxr it always bogged down under load at high rpm, ended up being one sparkplug breaking down and a dodgy plugcap.
 

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Discussion Starter · #14 ·
are you sure its the carbs causing the bogging down?
when i got my zxr it always bogged down under load at high rpm, ended up being one sparkplug breaking down and a dodgy plugcap
95% sure. I changed all of the plugs to brand new stock NGK's, all of the caps looked good.

Also, it only started bogging after I changed the carb settings closer to what other people with the same Jets had. (Before, it would stutter from 2,500rpm until 5,000rpm, now it runs pretty smooth through all of the RPM range, but bogs on low rpm.) So, I'm going to sync the carbs and test again, and if it's not better I will increase the float height, then sync and re-test. If THAT doesn't do it I will lean out the pilot screw 1/4 turn at a time, sync, and re-test after each.

Still need to know which carb adapter tubes I need. Motion Pro makes 5mm and 6mm tubes, anyone know which of those works for a zx7r?
 

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The hollow vacuum screws with nipples should be 6mm thread, but you just need to take one of your bike's plugs down to a hardware store to match it up.

CarbTune Pro ($85) comes with two plastic sets, but I've never had to use them. Both my bikes have all their vacuum and emissions plumbing intact and the hoses slip on and off easily enough. My 9s are also not jetted like what other people set them at. Probably why the bikes are admired by all those who ride them. :evil

Can't imagine how far off the TBs would have to be to cause low RPM bogging, but not affect high RPM. :headscratch
 

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jet

im running 15.5 mm floats with the kleen air crap removed but the mains you guys are running are huge...iv mine down to 132 mains and it pulls like a train. anything above 132 and it splutters at 5k and wont pull low down..
 

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Oh, I thought the order was:

Check valve clearances and shim as needed.
Make sure there are no intake/vacuum/fuel leaks.
Tune carbs (jets, needles, pilot screws).
Sync carbs.

I was under the impression that syncing the carbs is the last step because any changes to anything else can throw the sync off. Or is that true, but you also need to sync them after every tuning step before testing each tune?
Yes syncing is generally considered the last step when making any turning related changes. However I was recommending starting with the easiest thing possible as it may turn out you don't have a tuning problem rather just a sync issue.
 

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im running 15.5 mm floats with the kleen air crap removed but the mains you guys are running are huge...iv mine down to 132 mains and it pulls like a train. anything above 132 and it splutters at 5k and wont pull low down..
You must be running Dynojet mains, not Kiehen. THey use a different numbering system so don't confuse the two.
 

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...iv mine down to 132 mains and it pulls like a train. anything above 132 and it splutters at 5k and wont pull low down..
Your results of having the mains set right and it pulling like a train is because you think deductively and know the difference between a positive result and a negative result. That's not how we Americans do it. See, we ask others what they're running and follow. We especially like putting in the biggest jets we can find, because big jets deliver a lot of fuel and it's cool to tell others that we're running huge mains. ***The look in their eyes means they're impressed *** Then we spend the next year or so tinkering with all the wrong settings, trying to figuring out why our performance machine doesn't perform, instead of trial and error jet tuning like Factory Pro spells out in plain English; DO THIS!!! Soon after we sell it and move on, never knowing or understanding why we never got it right.

As you can imagine, our way is better. :evil
 
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