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Discussion Starter · #1 ·
Hi all,
I still own my baby and after a long time I decided to work on the carb tuning.

Here's what I did so far:
  • removed the Kleen stuff (putting a pipe instead of the two plates)
  • installed a full exhaust system made by shark in the 90s (it's for the K model but it does fit pretty well)
  • installed a Factory Pro Ti needle but not the main jets: I preferred an original Keihin 150-160-160-150 setup as advised by many sources
  • installed a +4 deg. advance kit
  • installed a BMC airfilter
  • airbox screen removed and sealed all the holes except the one close to the carbs (bottom), where I'm picking up air for the carb vent pipe (float bowl vent mod)
  • spark plug with double electrode (CR9EK)

and:
Float height is stock
air screw is 2.5 turns
Now the bike is really screaming from 3000 to 8000RPMs at WOT, no flat spots and the power is delivered very consistently.
Sometimes she idles a bit higher and after a while getting lower, so not always stable.
And here is the issue: @ WOT after 9000-10000RPMs she has an hesitation and runs irregularly. Not reaching the redline smoothly and I did not insist (it seems leaning out but not totally sure)

I've read a lot on many different sites and I am totally confused.

Before reaching out a shop for a dyno run and checking the AFR, I'd like to have you opinion on that.

I'd like to understand what the float height does and if it might have an impact here (is it leaning out when the RAM effect is building up?) I read somewhere that it should affect only idling and low-midrange but I'm not sure.

float bowl vent mod: I plugged the carb vent pipe to the lower nipple of the airbox (the rubber one that has a 90° bent). Should I use take the air pressure from any other nipple of the airbox (i.e. the original hole on the right hand side where the pipe slides in with no gasket at all?) I thought it might not be enough pressurized given the location of this nipple... who knows.

previously I was running a 160-170-170-160 main jet config and the spark plugs were (not soaked) but quite black (see the picture; I also scratched the exhaust can with the paper to check the colour). that is why I wanted to go down with the size to the current setup. I am quite surprised that the FP kit goes with a big size main jet kit (around 180) that sounds too rich like the stock 170-190-190-170 config.

I'd really appreciate if anyone can post a picture of the modded airbox for a 93-95 ZX7R (or ZXR as known in EU).

thanks all for any advice!
Light Spark plug Nozzle Plumbing Fastener
 

· Registered
1993 Zx-7 L Model, 2006 ZX-10R
Joined
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5,025 Posts
Hi all,
I still own my baby and after a long time I decided to work on the carb tuning.

Here's what I did so far:
  • removed the Kleen stuff (putting a pipe instead of the two plates)
  • installed a full exhaust system made by shark in the 90s (it's for the K model but it does fit pretty well)
  • installed a Factory Pro Ti needle but not the main jets: I preferred an original Keihin 150-160-160-150 setup as advised by many sources
  • installed a +4 deg. advance kit
  • installed a BMC airfilter
  • airbox screen removed and sealed all the holes except the one close to the carbs (bottom), where I'm picking up air for the carb vent pipe (float bowl vent mod)
  • spark plug with double electrode (CR9EK)

and:


Now the bike is really screaming from 3000 to 8000RPMs at WOT, no flat spots and the power is delivered very consistently.
Sometimes she idles a bit higher and after a while getting lower, so not always stable.
And here is the issue: @ WOT after 9000-10000RPMs she has an hesitation and runs irregularly. Not reaching the redline smoothly and I did not insist (it seems leaning out but not totally sure)

I've read a lot on many different sites and I am totally confused.

Before reaching out a shop for a dyno run and checking the AFR, I'd like to have you opinion on that.

I'd like to understand what the float height does and if it might have an impact here (is it leaning out when the RAM effect is building up?) I read somewhere that it should affect only idling and low-midrange but I'm not sure.

float bowl vent mod: I plugged the carb vent pipe to the lower nipple of the airbox (the rubber one that has a 90° bent). Should I use take the air pressure from any other nipple of the airbox (i.e. the original hole on the right hand side where the pipe slides in with no gasket at all?) I thought it might not be enough pressurized given the location of this nipple... who knows.

previously I was running a 160-170-170-160 main jet config and the spark plugs were (not soaked) but quite black (see the picture; I also scratched the exhaust can with the paper to check the colour). that is why I wanted to go down with the size to the current setup. I am quite surprised that the FP kit goes with a big size main jet kit (around 180) that sounds too rich like the stock 170-190-190-170 config.

I'd really appreciate if anyone can post a picture of the modded airbox for a 93-95 ZX7R (or ZXR as known in EU).

thanks all for any advice!
View attachment 21851
Adjust your fuel mixture screws to 2 half turns out and test the idle at operating temp.
Do you have another air filter to try? I know the BMC filters are pretty porous and allow for more flow.
 

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Discussion Starter · #3 ·
Adjust your fuel mixture screws to 2 half turns out and test the idle at operating temp.
Do you have another air filter to try? I know the BMC filters are pretty porous and allow for more flow.
ok. I guess the change to the mixture screws should affect the idling right?

Re. the air filter, this is the street version which is in line with K&N. The BMC Race filter was too much for a street use...
Anyway I can probably get a stock one if you think it's worth trying.
thanks
 

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1993 Zx-7 L Model, 2006 ZX-10R
Joined
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5,025 Posts
ok. I guess the change to the mixture screws should affect the idling right?

Re. the air filter, this is the street version which is in line with K&N. The BMC Race filter was too much for a street use...
Anyway I can probably get a stock one if you think it's worth trying.
thanks
Well, your top end fueling is too much (probably. by looks of your spark plug). I was thinking you either need the race filter, a fatter needle or a smaller main jet.
 

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Discussion Starter · #5 ·
ok that is exactly what I thought that led me to lower the main jets from 160-170-170-160 to 150-160-160-150.

so the issue at high revv must be something else then the jets....

in the meantime I found this in the 92 race manual.
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1993 Zx-7 L Model, 2006 ZX-10R
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ok that is exactly what I thought that led me to lower the main jets from 160-170-170-160 to 150-160-160-150.

so the issue at high revv must be something else then the jets....

in the meantime I found this in the 92 race manual.
View attachment 21852
I'm an idiot. Did you change the main air jets or the main fuel jets?
 

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Discussion Starter · #12 ·
The kit manual is for the R model with FCR carbs. Make sure the carb vent line is on the pressurized side of the air box or it will lean out at the top end.
yes sure, I realized that. I was only realizing what is affecting what.

Not sure to understand what you mean here:

Make sure the carb vent line is on the pressurized side of the air box or it will lean out at the top end.
do you mean that the vent line goes before the airfilter? not sure I'm getting it right

thanks
 

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Discussion Starter · #13 ·
probably I'm not really able to explain...
let's add a picture
Hood Automotive design Automotive lighting Input device Motor vehicle


As of now I've plugged the air vent where you see the blue arrow (there is a rubber pipe that goes in there)

Or should I use the hole with the red arrow?

thanks once more!
EDIT: here below the hole I used for the vent
Luggage and bags Bag Gas Electric blue Camera accessory
 

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Discussion Starter · #19 ·
ok so I started the work and here's how's today
Hood Motor vehicle Automotive design Automotive exterior Auto part



so disconnecting these pipes and I'll hook these two up together (after removing the epoxy seal I did)
Motor vehicle Automotive tire Automotive lighting Automotive design Rim



btw in the meantime this is how the spark plug looks like after re-jetting.
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Liquid Finger Automotive tire Tints and shades Gas

it seems a little bit on the lean side, probably due to the wrong float bowl mod I did.
I will keep this setup and re-test when the new vents line will be installed.

apologies for the big pictures, I should have resized before posting.

Cheers
 

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1993 Zx-7 L Model, 2006 ZX-10R
Joined
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5,025 Posts
ok so I started the work and here's how's today
View attachment 21878


so disconnecting these pipes and I'll hook these two up together (after removing the epoxy seal I did)
View attachment 21879


btw in the meantime this is how the spark plug looks like after re-jetting.
View attachment 21880
it seems a little bit on the lean side, probably due to the wrong float bowl mod I did.
I will keep this setup and re-test when the new vents line will be installed.

apologies for the big pictures, I should have resized before posting.

Cheers
I enjoy big pictures
 
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